Sheldon Brown photo

Sheldon Brown's Bicycle Glossary B

Search sheldonbrown.com Search sheldonbrown.org Search WWW

A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z

Up to previous page

Bolt Circle Diameter (B.C.D.)

On a crank set, the diameter of the circle formed by the stack bolts.

Standard double chainwheel sets use 130 mm or 110 mm diameters.

Modern triple chainwheel sets have two diameters, a large one for the two outer chainrings, and a smaller diameter, with a separate set of bolts, for the granny ring.

Full-size triples usually use 110 mm/74 mm, or 130 mm/74 mm for newer "road triples." Campagnolo uses 135 mm/74 mm. Compact triples commonly use 94 mm/58 mm.

Some crank sizes:

"C-C" is the distance between adjacent stack bolts.
This is easier to measure directly than the actual Bolt Circle Diameter.

Measuring Bolt Circle Diameter

Measuring BCD: This 110 mm BCD ring measures 64.7 mm center-to-center.

Multiplying this dimension by 1.7 will give you the actual BCD for a 5 bolt chainring.

Use 1.4 for 4 bolt chainrings
5 Bolt Cranks:
BCD (mm) Smallest
Ring
Center-Center
(mm)
Application
1514488.8Very old Campagnolo standard (pre '67) (Obsolete)
1444184.6Old Campagnolo standard, still used for track applications.
1353979.5Current Campagnolo standard
1303876.4Standard Road double and triple (outer 2)
1283875.2Nervar (Obsolete)
1223871.7Stronglight 93, others (Obsolete)
1183669.4Ofmega, SR (Obsolete)
1163568.2Old Campagnolo (Obsolete)
1103364.7Touring double, standard triple outer
942955.4Compact triple outer
923053.3Shimano Dura-Ace triple inner.
862850.5Stronglight 99, some SR triples. (Obsolete)
742443.5Standard ("full-sized") triple inner, used with 110 mm, 130 mm or 135 mm rings.
582034.3Compact granny
562032.9Sun Tour Compact granny (Obsolete)
4 Bolt Cranks:
BCD (mm) Smallest
Ring
Center-Center
(mm)
Application
14644103.2Shimano XTR M960 Hollowtech 4-arm outer
1123479.2Shimano XTR M950, M952 4-arm middle/outer
1043273.6Shimano XTR M960, XT, LX 4-arm outer
682248.1Shimano XTR M950, M952 4-arm inner
642245.3Shimano XTR M960, XT, LX 4-arm inner

Bolt

A fastener with male threads, usually with a hexagonal head. Strictly speaking, it's only a bolt if the threads do not extend the full length of the shaft.

If the threads do extend full length, technically it is a "screw " but only pedants insist on this distinction.

Bolt-on

Slang term for a non-quick release hub or axle. More properly, these should be referred to as "nutted" or "solid axle" units, since conventional hubs use nuts, not bolts.

A very few high-end hubs actually do use bolts, usually with an Allen head. Among these are American Classic, Bullseye, Phil Wood and White Industries.

Bone Shaker

The earliest type of bicycle, from the mid 19th century. A boneshaker had wheels of roughly equal size, like a modern "safety" bicycle, but the pedals were directly connected to the front hub, as with a high wheeler.

Boneshakers existed before the invention of Dunlop's pneumatic tire, and had wood or iron wheels, with iron or (later) solid rubber tires. This caused them to provide a very harsh ride, hence the name.

The bone shaker evolved over time into the high wheeler, with the drive wheel getting larger and larger, the rear wheel shrinking down.

Boob tube

A television set. (Boob: "A stupid or foolish person; a dolt" (who watches too much TV); Tube: the cathode ray tube of a TV receiver.)

Some misguided souls use this term to describe the keel tube of a tandem frame. This makes no sense semantically. It probably arose because somebody couldn't think of one of the several more descriptive terms, and picked somthing cute sounding out of the air. It is to be hoped that this foolish term will disappear into the dustbin of history.

Boom tube

Keel tube. Also, the tube (often adjustable by telescoping) that holds the "bottom bracket" on a short-wheelbase recumbent.

Booster

The bosses of cantilever brakes can flex outward when the brake is applied hard. This contributes to a "spongy" feeling to the brake lever, and, in some cases, the extra flex may permit the brake lever to bottom out against the handlebar.

A "brake booster" is a metal bridge that connects the outer ends of the two cantilever bosses, holding them in position and greatly reducing their tendency to flex under load. A booster resembles an inverted "U", as it curves up and over the tire.

Boot

Boss

A bump or protrusion. This term has several specific bicycle usages:

Boston Montréal Boston

Boston Montréal Boston is North America's premiere randonée, the North American equivalent of Paris Brest Paris.

Bottom bracket

The part of the frame around which the pedal cranks revolve, also the bearings and axle assembly that runs through the bottom bracket shell of the frame.

A conventional cup-and-cone bottom bracket. The lock ring wrench is about to loosen the lockring, the pin wrench is engaging two of the holes in the adjustable cup A cartridge bottom bracket. The splined tool is shown above the bottom bracket. The crank would need to be removed to actually use the tool. Old American-style "Ashtabula" One-piece Crank Bottom Bracket
The lock nut and the cone behind it have a left-hand thread .
Three piece adjustable cup-and-cone bottom bracket Three piece sealed cartridge bottom bracket American Ashtabula one-piece crank bottom bracket
An old American term for "bottom bracket" is "hanger". This is usually used in connection with one-piece cranks.

Bottom brackets come in different sizes, according to the nationality of the frame:

Standard:ThreadingAdjustable
(left) cup
direction
Fixed
(right) cup
direction
Shell
Width
Applications/Notes
British
I.S.O.
1.370" X 24 tpi
1.375" X 24 tpi
rightleftStandard 68 mm
O.S. 73 mm
The overwhelming majority of bicycles in current production.
British and I.S.O. are interchangeable.
ISIS Overdrive48 x 1.5 mmrightleft68mm
100 mm
New proposed standard oversized system.
Italian36 mm X 24 tpirightright
(wrong!)
70 mmItalian and some high-end French bicycles.
Prone to problems due to the right threaded fixed cup,
which tends to unscrew itself in use.
French35 mm X 1mm (25.4 tpi)rightright
(wrong!)
68 mmObsolete, used on older French bicycles.
Prone to problems due to the right threaded fixed cup,
which tends to unscrew itself in use.
Swiss35 mm X 1mm (25.4 tpi)rightleft68 mmSame thread as French, but fixed cup is left threaded for reliability.
Raleigh1 3/8" X 26 tpirightleft71mm
76 mm
Older British-made Raleighs, especially 3 speeds.
O.P.C.
Ashtabula
Male threads
on crank
24 tpi (most)
28 tpi
(Schwinn,
Mongoose)

68 mm (2.68") wide
51.3 mm (2.02") i.d.
(approximate)
Older U.S. bikes, BMX, Juvenile bikes,
Department store bikes.
24 tpi cranks use #66 retainers, with 10 5/16" balls.
28 tpi cranks use #64 retainers, with 9 5/16" balls.

What happens if you try to mix different sizes:

Bottom Bracket
Shell Threading
(Below)
BritishI.S.O.
1.37/1.375" x 24 tpi CUPS R-L
(34.8/34.9 x 1.06 mm)
Italian
36 mm X 24 tpi CUPS R-R
(1.417" x 1.06 mm)
French
35 mm X 1mm CUPS R-R
(1.378 x 25.4 tpi)
Swiss
35 mm X 1mm CUPS R-L
(1.378 x 25.4 tpi)
Raleigh
1 3/8" X 26 tpi CUPS R-L
(34.9 x 1.06 mm)
British/I.S.O.
1.37/1.375" x 24 tpi
(34.8/34.9 x 1.06 mm)
Made to Fit 36 mm Cup diameter is too large, thread won't even start. Cup diameter is slightly too large, usually won't start.
Right (fixed) up threaded in the opposite direction.
Cup diameter is slightly too large, usually won't start. Diameter matches, but thread pitch does not.

Will bind after only a few threads are engaged.

Italian
36 mm X 24 tpi
(1.417" x 1.06 mm)
British/I.S.O. cups fall through Made to Fit Italian shells are larger diameter, all other size cups fall right through, threads will not engage.
French
35 mm X 1mm
(1.378 x 25.4 tpi)
35 mm = 1.378". Shell is slightly larger, thread pitch slightly finer.
Left side may seem to fit, but will be loose.
36 mm Cup diameter is too large, thread won't even start. Made to FitLeft (adjustable) side is interchangeable.
Right (fixed) side is threaded in the opposite direction, won't fit.
35 mm = 1.378". Shell is slightly larger, thread pitch slightly coarser.
Left side may seem to fit, but will be loose.
Swiss
35 mm X 1mm R
(1.378 x 25.4 tpi)
35 mm = 1.378". Shell is slightly larger, thread pitch slightly finer. May seem to fit, but will be loose. 36 mm Cup diameter is too large, thread won't even start. Left (adjustable) side is interchangeable.
Right (fixed) side is threaded in the opposite direction, won't fit.
Made to Fit 35 mm = 1.378". Shell is slightly larger, thread pitch slightly coarser.
May seem to fit, but will be loose.
Raleigh
1 3/8" X 26 tpi
(34.9 x 1.06 mm)
Diameter matches, but thread pitch does not.

Will bind after only a few threads are engaged.

36 mm Cup diameter is too large, thread won't even start. Cup diameter is slightly too large, usually won't start.
Right (fixed) up threaded in the opposite direction.
Cup diameter is slightly too large, usually won't start. Made to Fit

Chainline Standards:

ApplicationDimensionNotes
Road Double43.5Shimano spec, measured to the midpoint between the rings.
with typical 5 mm chainring spacing, this puts the inner at 41 mm, the outer at 46 mm.
Road Triple45Shimano spec, measured to the middle ring.
MTB Triple47.5-50 mmShimano spec, measured to the middle ring.
47.5 preferred, but for frames with oversized seat tubes, the longer dimension may be needed, because the fat tube places the derailer mechanism farther to the right.
Track/Coaster Brake
Traditional One-Speed
Most internal gear hubs
40.5-42 mmOlder bikes with 110 spacing would be on the smaller end of this range
Newer bikes with 120 mm spacing normally use 42 mm
Singlespeed MTB52 mm Wider chainline need for chainstay clearance on MTBs.

This is close to the chainline of the outer ring of a typical MTB triple

Rohloff Speedhub54 mm
(58 mm w/13 tooth)
Singlespeed MTB
Alternate
47.5 mmWhite Industries ENO hubs use this chainline, which lines up with the middle position of a typical MTB triple.
It's also fairly close to the outer position of a typical "road" double.

Standard bottom bracket bearing assemblies are specified in terms of width of the bottom bracket shell (generally 68, 70 or 73 mm) and the length of the spindle (102 - 130 mm.)

Current usage generally assumes that 68 and 73 mm bottom bracket units are for British/ISO threaded frames, and that 70 mm units are for Italian threaded frames.

The spindle length mainly depends on that kind of crankset you'll be using, and doesn't have much to do with the frame. New cranks come with a spec sheet that lists what length spindle they are intended to be used with. Sometimes two lengths are listed. When this is the case, the longer size is for use on frames with fat seat tubes, because such frames put the front derailer mechanism farther to the right than it is on a frame with a standard seat tube.

See also my article on Bottom Bracket Sizes for information on matching spindles to cranks.

See also my article on Bottom Bracket Tapers.

My Tool Tips series includes related articles on Cottered, and Cotterless crank removal, as well as tools for dissasembly and adjustment of cup-and-cone bottom brackets.

Bottom Pull

See Top pull.

"Boutique" Parts

Most of the best bicycle parts are made by a few major companies, who provide excellent value thanks to good design and economies of scale resulting from large scale mass-production.

In the bicycle industry, the best frames have traditionally been made by very small scale, custom or semi-custom framebuilders.

There are also small-scale makers of premium or super-premium parts, companies such as Chris King, E.A.I., Phil Wood , White Industries and a few others. These small, high-prestige manufacturers often (but not always) make products superior to those of the big manufacturers. For instance, Chris King headsets are the very best, and Phil Wood hubs and bottom brackets are unequalled.

Unfortunately, the "boutique" category also includes a lot of other companies who produce overpriced, inferior products, or sometimes just slap prestigious name on generic Asian imported stuff.

"Boutique" hubs

When a company wants to get started making bike parts, hubs, especially front hubs or singlespeed/track hubs are the easiest thing to make. There are many boutique and off-brand hubs out there.

Boutique hubs are often sold on the basis of light weight, but that's often a bit of a scam. Boutique hubs are generally sold without quick release skewers , while major brand hubs come with skewers. This has two negative effects:

Boutique hubs are commonly CNC machined out of bar stock, so the "grain" of the metal is perpendicular to the hub flanges.

Major brand hubs have forged bodies, making the spoke flanges considerably stronger.

"Boutique" hubs are often marketed as if they were an upgrade from, say, run-of-the-mill Shimano hubs, but in fact they are generally inferior in quality to genuine Shimano hubs! (The only hubs that I consider actually superior to Shimano are Phil Wood, and they typically cost at least three times as much as Shimano.)

"Boutique" wheels

Many newer bikes come with "premium" wheels with reduced numbers of spokes. Basically anything fewer than 32 or 28 spokes per wheel would fall into this category. These wheels are touted as being faster due to improved aerodyamics, and many people assume that the reduced number of spokes makes them lighter. In practice, these wheels are actually heavier than good traditional wheels! The reason is that when ou use fewer spokes, you need to use a stronger, stiffer, heavier rim to make an acceptably strong wheel.

These wheels are basically throw-away items, intended to be used for a season or until they get damaged, then replaced with a new set.

Bowden Cable

The type of concentric cables used for brakes and gears was once known by the term "Bowden cables", after their inventor.

There was a famous legal case arising from Bowden's cables. He licensed many manufacturers to manucfacture cables based on his patent, but failed to exercise quality control over the licensed products that bore his name. As a result, the patent and trademark were deemed to have been abandoned, and became public domain. (I am not a lawyer, I heard this from a lawyer some time ago, I don't vouch for the accuracy of the legal information...)

Brake

Caliper, Cantilever, Centerpull, Coaster, Direct Pull, Disc, Double pivot, Drum, Dual pivot, Roller, Rollercam, Roller lever, Sidepull, Single pivot, Spoon, "V-Brake" ®:

Brake bridge

The short length of tubing connecting the seatstays just above the tire. This is the usual mounting point for a rear caliper brake.

Brake Lever Types

Brake levers (handles) for use with cable operated brakes come in 4 basic types.

The differences depend on the handlebar type they are to be used with, and on the amount of cable travel required:

Handlebar Type

Levers for drop ("road" "racing") handlebars curve toward the handlebar, to follow the curvature of the handlebar. These levers also mounting clamps to fit the 23.8 mm (15/16") diameter of almost all drop handlebars.

Levers for upright ("mountain" "cruiser" "BMX") handlebars mount on a straight section of the handlebar, and the lever curves away from the bar for better clearance. These levers have mounting clamps to fit the 22.2 mm (7/8") diameter of almost all upright handlebars.

Cable Pull

Standard pull levers are designed to work with caliper brakes or traditional center-pull cantilever brakes.

Long pull levers are designed to work with "direct-pull" cantilever brakes, such as Shimano "V-Brakes" ®

Direct pull cantilevers have twice as much mechanical advantage as traditional brakes, so they require a lever with half as much mechanical advantage. Long pull levers pull the cable twice as far, but only half as hard.

Mismatched Lever Issues:

Old short-pull lever, new direct pull ("V type") cantilever

The excessive mechanical advantage of this combination will make it difficult to modulate the brake, and it may be all too easy to lock up the wheel.

The lever feel will be very soft and mushy.

The lever will travel too far before engaging the brake, and it may bottom out against the handlebar. Thus, the brake may be super powerful at first, but as the brake shoes wear, the lever bumping up against the handlebar will prevent full application. This is likely to be a particular problem in wet conditions.

New long-pull lever, old caliper or traditional cantilever

The reduced mechanical advantage will require unusually high hand strength to get barely adequate braking force.

Paradoxically, the lever will feel very solid, the brake will engage with a very short amount of lever travel...but won't actually be squeezing very hard on the rim.

Most disc brakes are designed for long-pull levers, but discs designated as "road" models are usually compatible with traditional short-pull levers.

There are stepped pulley devices to permit mixing otherwise incompatible levers/brakes. The best known is the QBP Travel Agent ®.

Brass

An alloy of copper and zinc, in the proportion of about two parts of copper to one part zinc. The zinc makes brass stronger and harder than copper is alone. It is easy to work, and doesn't rust. Most spoke nipples are made of brass, because it is easy to thread and will not rust to the spoke threads.

Brass is also easy to cast, and has been used for derailer parts and quick-release skewer acorn nuts, and for thrust washers in caliper brakes. Various special brass alloys are used as filler material for brazing.

Braze-on

A small fitting permanently attached to a frame. On traditional steel frames these attachments are held on by brazing, but the term "braze-on" is also used for fittings that are welded, glued, rivetted or moulded on to frames of other materials. Typical braze-ons would include cable stops and guides, water bottle cage mounts, shift lever bosses, cantilever brake bosses and cable stops, pump pegs, etc.

Brazing

Brazing is the joining of metal parts by melting a different metal (of lower melting point) which bonds the parts together. Typically brazing involves joining steel parts with molten brass. Soldering is a similar operation, using lower temperatures and different filler metals (with a lower melting point) In brazing and soldering, the filler metal penetrates inaccessible areas of the joint by capillary action.

See also welding, fillet brazing.

Breaker Bar

***** wrench

Brevet

A randonnée to qualify a rider to enter a longer randonnée.

This is a French word, variously translatable as "diploma," "certificate" or "patent."

Bridgestone

Bridgestone is an enormous multinational company, one of the largest tire companies in the world...and a fairly small bicycle company, with its own factory in Japan. In the late 1980s and early'90s, their U.S. bicycle division was run by Grant Petersen, a brilliant, talented and idiosyncratic designer.

Petersen, a hard-core cyclist, marched to a "different drummer" than most of the industry. He introduced many innovations to the market, and also strongly resisted other trends and innovations that he didn't approve of. He is now the head of Rivendell Bicycle Works.

Bridgestone bikes are something of a cult item now. This site includes a whole subsection on Bridgestone bikes.

Brifter

A combination brake/shift lever, such as a Campagnolo Ergo or Shimano S.T.I. unit. This term was coined by Bruce Frech.

Brinelling

The dents that sometimes develop in headsets are often colloquially refered to as "brinelling" from the resemblance to the dents made by the Brinell Hardness Test.

Sometimes the term is (somewhat inappropriately) applied to damaged headset races.

See JobstBrandt on "Indexed Steering"

Brinell Hardness Test

At the begining of the last century Johan August Brinell, a Swedish Metallurgist, proposed a rapid, standard method of measuring the hardness of metallic materials. The method as most commonly applied consists of indenting a surface with a 10 mm hard steel ball with a 3000kg load for 30 seconds. The Brinell Hardness Number (BHN) is then measured by measuring the diameter of the indentation using a straightforward formula (or usually plucked off of a chart).

The load is reduced to 500kg for very soft materials and the steel ball is replaced with tungsten carbide for very hard materials. Substantial section thicknesses are required to ensure that the test is "valid", that is, edge effects or gross section deformation remain negligible.

As a standardized test, the procedure is very useful in industrial settings, primarily as a quality control tool. In common steels, as a rule-of-thumb BHN * 515 is approximately equal to the ultimate tensile strength.

The test is useless in the context of bicycles since almost no part of a modern bicycle would survive intact the effect of a 10 mm ball at 3000kg and no part of a bicycle is sufficiently massive to ensure a "valid" test.

The BHN number, albeit a very useful tool in manufacturing, is not a satisfactory physical constant nor is it applied to design. Also, the BHN number is not reproducible under nonstandard ball diameters and loads unless geometric similitude is maintained.

Other hardness tests have largely replaced the Brinell Test.

(This definition contributed by John Fox)

British

In the early days of bicycle manufacture, every industrialized country had its own system of thread sizes and standard dimensions for bicycle parts. The British system is the one that has, by-and-large, prevailed. British dimensions have mostly been adopted by the I.S.O. These standards include:

Brodie

A maneuver consiting of locking the rear brake while turning, so that the rear wheel oversteers and the bike comes to a stop in a cloud of dust, while turning up to 180 degrees. Usually performed with the inboard foot off the pedal and extended inward to act as an outrigger.

Brooks

The world's foremost maker of leather saddles. Brooks is based in England, and is one of the oldest companies in the bicycle industry. They were formerly also the leading maker of English-style touring bags.

B.R.S.

Balanced Response System. Dia Compe's system of adding a weak return spring to the brake lever. Since the cable was being pushed at one end and pulled at the other, a positive return function could be attained with a much lower overall spring tension. This greatly improved the "feel" and sensitivity of the brake.

B.S.A.

B.S.A. (Birmingham Small Arms) was a major British manufacturer of firearms, and later of bicycles and motorcycles. They reached their peak in the 1920's. The standard thread sizes that they developed for their bicycles were ultimately adopted as the standard British (B.S.C.) sizes, which, in turn, were mostly adopted by the I.S.O.

B.S.C.

British Standard Cycle. The standard dimensions pioneered by B.S.A. were ultimately adopted by the bulk of the British cycle industry under this designation.

B.S.D.

Bead Seat Diameter

BSX / Bicycle Supercross

Bicycle Supercross, an adult version of BMX, using mountain bikes on a downhill course similar to a BMX track.

Also known as "Four cross" or "4X" Mountain bike riders compete on a specially designed highly-challenging course. The races last between 25 seconds and one minute and are usually fast and frenzied. The courses are a mix of natural and man-made obstacles covering a steep descent.

The array of obstacles include triples, doubles, table tops, step ups, drop offs, bermed or off-camber corners and gap jumps. The difficulty of getting over these obstacles at high-speed whilst being jostled by three other competitors means there are plenty of crashes. The 4X competition starts with a limited number of riders competing in knock-out rounds.

The knock-out rounds can be decided by a series of heats called 'Motos' with riders competing three times before moving on to quarters, semis and final. The final consists of the last four riders left in the competition.

Matt Andrews

Bull Horn Handlebar

See "Cow Horn."

Bull Moose Handlebar

A style of handlebar popular on early mountain bikes. The handlebar and stem are a single unit, with the stem splitting in two at the quill and attaching to the handlebar at two points, forming a triangle.
image

Bungee, Bunji, Bungie, Bungy...nobody knows how to spell it

An elastic shock cord with hooks on the end, commonly used for securing baggage to a luggage carrier. Also known as a "Sandow".

Burley

A manufacturing co-op, based in Eugene, Oregon. Burley is a leading manufacturer of tandems, trailers and rain gear.

Busch & Müller

A German manufacturer best known for their "Nabendynamo" generator hub.

Bushing

A hollow cylindrical part that connects two other parts, usually serving as a simple bearing. A bushing may have a stepped outer circumference to locate the outer part axially.

Butted

Thicker at the ends. Said of spokes and frame tubing. (Butted spokes are also called "swaged") Butted tubing is usually made with a constant outside diameter, but thicker walls at the ends. The idea is to make the part stronger at the ends, where the stresses are greatest, and lighter in the long middle section, where stresses are less.

Some writers have objected to this term being applied to spokes, and maintain that "swaged" is more correct, since the operation that produces a butted/swaged spoke is one of thinning the middle, not thickening the ends. For some reason they don't generally object to the use of "butted" in reference to tubing, though the process is also one of thinning the middle, not thickening the end. This objection is based on a misunderstanding of the origin of the origin of the term "butted." "Butted" means having a butt, i.e. a thick end, and has no reference to the means of fabrication.

Down to next page

A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z

Spoke Divider

Feedback? Questions?

Articles by Sheldon Brown and others
Harris
Home
Beginners Brakes Commuting
Lights
Cycle-
Computers
Do-It-
Yourself
Essays
Family
Cycling
Fixed Gear
Singlespeed
Frames Gears &
Drivetrain
Bicycle
Humor
Bicycle
Glossary
Bicycle
Links
Old
Bikes
Repair
Tips
Tandems Touring What's
New
Wheels Sheldon
Brown

Accessories Bicycles Parts Specials Tools

Since May 4, 1996

Copyright © 1996, 2008 Sheldon Brown

Back to Harris Cyclery Home Page

If you would like to make a link or bookmark to this page, the URL is:
http://sheldonbrown.com/gloss_bo-z.html

If you would like to make a link or bookmark to this glossary, the URL is:
http://sheldonbrown.com/glossary

If you would like to make a link or bookmark to a specific definition, that's fine too. I am committed to keeping the urls stable, so I won't be breaking your link.

blank