Home

  

Tapped Threads

Refer to Introduction to Taps, pages one & two.
See Threading Section & How to Drill a Hole.

A hand tapping fixture allows precise, perpendicular, tap-to-hole alignment plus it reduces
 tap breakage that can easily occur when too much torque and/or side forces are applied.
The Phase2+ tapper is a superior product in terms of design, material & workmanship.
Hand tapper
includes a set of adapters: #6, #8, #10,
¼", 5/16", 3/8", 7/16", ½" and 5/8".
The tap is first fixed to the adapter & then snapped into the spindle.
If the adapter is snapped in without a tap, it can be more easily removed by
first rotating the flat detent spring to release the ball bearing detent.
Be careful to not lose the ball detent.

Tap Capacity #6 to "
Table to Bracket 7-"
Spindle to Bracket 7-½
Table 6” x 12-½
Spindle Diameter 1"
Weight 40 lbs.


Detail of the spring-loaded ball bearing detent for adapter retention in the precision ground spindle.
The flat spring has been rotated to expose the ball bearing detent.
The vise is allowed to float in two directions enabling easy tap/hole alignment.
The example shows tapping eight, #7 holes, with ¼-20 threads.
A rotary table was used to drill every 45°.

To steady the hand tapper, 5/16-18 SS bolts screw into bench hard points.
The ¾" holes were drilled using a Forstner bit. The hard points are held in underneath by wood screws.
I remove the tapper when not in use & screw the bolts up from the bottom until they are flush.
The bolt-down hole has also been
-16 threaded to use the clamping studs, as needed.



Always chamfer the hole first & use the proper thread-cutting fluid.
Caution: For soft materials (aluminum, brass, plastic) use a smaller hole for 75% threads & for
harder materials (steel, SS) use a larger tap hole for 50% threads to reduce tap breakage. See table, below.
Certain materials, e.g., cast iron, can crumble, so coarse threads are easier to
cut more successfully than fine. Softer steels can have higher percentage threads (in the 60s).
There are formulae for calculating any desired % threads.


The adapter has a round hole with a set screw to hold in the tap &
a square hole at the end to positively engage the tap end to prevent rotation.
Note the recess for the spring-loaded detent. A spiral-fluted bottoming tap is shown.

This is a small hand tapper with adapters for seven different tap sizes 0-80 through 5/16".
Each hex-shaped adapter has a square hole & a set screw to securely engage & hold the tap shank.
The shaft rotates in a pressed-in brass bearing. The chromed, stop pin can be removed to
provide more table room for the vise/part. The pin's hole can also be used to bolt-down to a bench hard point.
The steel table is 8.5" x 6", the clearance height is 3.75", the throat depth is 4.5", & the overall height is 9".

This example shows a 0-80 tapping operation where a 3/64" tap hole is required for a 75% thread.



Tapping (6-32) a brass weight.

Differently sized tap wrenches.
Top two are Sears, the middle one is Irwin & the bottom two are LS Starrett.
The Starrett handles are of superior design & quality.
Use a tapping guide block to keep the tap perpendicular when hand tapping.
The series of holes match the standard tap diameters.

 


 

 

Tap wrenches of various sizes.
The two black wrenches (left) have integral guides that mount in a drill press, mill, or lathe.
The ratchet-type tap wrench (right of center) is useful in tight places.
Tap wrenches usually have a center-drilled hole on its end that can be used with a guide.
Smaller taps, themselves, have a chamfered (pointed) shank end &
larger taps have a center-drilled hole to use with guides.

 

 


The micro-tap guide (top) has a hardened, reversible tip. The pointed end fits into a center drilled tap wrench end &
the cupped end captures/guides the shank end of the tap, itself. Both have adjustable spring tension.
A Taig spring-loaded center is shown (bottom) that also works well as a tap wrench pivot.
A spring-loaded guide semi-automatically adjusts as the tap cuts deeper into the hole.

 


This tap handle slides on a steel rod & the 1" diameter handle that does not easily over torque the tap.
The long, precision fitted guide rod gives excellent, rigid support.

 


Die handles. Top one is for 1-½" diameter dies ( split-type is shown) &
 the bottom one is for hex-style dies. A hex die-to-tap adapter is also shown.

 


Metric die & tap set.

 

Tap drill references for Imperial, metric, & pipe threads.
 

Imperial Tap Drill Chart

Machine Screw Size Number of Threads/Inch Minor
Diameter
Tap Drills Clearance Hole Drills
Aluminum, Brass & Plastics

75% Thread

Stainless Steel, Steels & Iron

50% Thread

All Materials
Close Fit Free Fit
No. or Diameter Major Diameter Drill Size Decimal Equiv. Drill Size Decimal Equiv. Drill Size Decimal Equiv. Drill Size Decimal Equiv.
0 .0600 80 .0447 3/64 .0469 55 .0520 52 .0635 50 .0700
1 .0730 64 .0538 53 .0595 1/16 .0625 48 .0760 46 .0810
72 .0560 53 .0595 52 .0635
2 .0860 56 .0641 50 .0700 49 .0730 43 .0890 41 .0960
64 .0668 50 .0700 48 .0760
3 .0990 48 .0734 47 .0785 44 .0860 37 .1040 35 .1100
56 .0771 45 .0820 43 .0890
4 .1120 40 .0813 43 .0890 41 .0960 32 .1160 30 .1285
48 .0864 42 .0935 40 .0980
5 .1250 40 .0943 38 .1015 7/64 .1094 30 .1285 29 .1360
44 .0971 37 .1040 35 .1100
6 .1380 32 .0997 36 .1065 32 .1160 27 .1440 25 .1495
40 .1073 33 .1130 31 .1200
8 .1640 32 .1257 29 .1360 27 .1440 18 .1695 16 .1770
36 .1299 29 .1360 26 .1470
10 .1900 24 .1389 25 .1495 20 .1610 9 .1960 7 .2010
32 .1517 21 .1590 18 .1695
12 .2160 24 .1649 16 .1770 12 .1890 2 .2210 1 .2280
28 .1722 14 .1820 10 .1935
32 .1777 13 .1850 9 .1960
¼ .2500 20 .1887 7 .2010 7/32 .2188 F .2570 H .2660
28 .2062 3 .2130 1 .2280
32 .2117 7/32 .2188 1 .2280
5/16 .3125 18 .2443 F .2570 J .2770 P .3230 Q .3320
24 .2614 I .2720 9/32 .2812
32 .2742 9/32 .2812 L .2900
.3750 16 .2983 5/16 .3125 Q .3320 W .3860 X .3970
24 .3239 Q .3320 S .3480
32 .3367 11/32 .3438 T .3580

7/16

.4375

14 .3499 U .3680 25/64 .3906

29/64

.4531

15/32

.4687

20 .3762 25/64 .3906 13/32 .4062
28 .3937 Y .4040 Z .4130
½ .5000 13 .4056 27/64 .4219 29/64 .4531 33/64 .5156 17/32 .5312
20 .4387 29/64 .4531 15/32 .4688
28 .4562 15/32 .4688 15/32 .4688
9/16 .5625 12 .4603 31/64 .4844 33/64 .5156 37/64 .5781 19/32 .5938
18 .4943 33/64 .5156 17/32 .5312
24 .5114 33/64 .5156 17/32 .5312
.6250 11 .5135 17/32 .5312 9/16 .5625 41/64 .6406 21/32 .6562
18 .5568 37/64 .5781 19/32 .5938
24 .5739 37/64 .5781 19/32 .5938
11/16 .6875 24 .6364 41/64 .6406 21/32 .6562 45/64 .7031 23/32 .6562

¾

.7500

10 .6273 21/32 .6562 11/16 .6875

49/64

.7656

25/32

.7812

16 .6733 11/16 .6875 45/64 .7031
20 .6887 45/64 .7031 23/32 .7188
13/16 .8125 20 .7512 49/64 .7656 25/32 .7812 53/64 .8281 27/32 .8438
7/8 .8750 9 .7387 49/64 .7656 51/64 .7969 57/64 .8906 29/32 .9062
14 .7874 13/16 .8125 53/64 .8281
20 .8137 53/64 .8281 27/32 .8438
15/16 .9375 20 .8762 57/64 .8906 29/32 .9062 61/64 .9531 31/32 .9688
1 1.000 8 .8466 .8750 59/64 .9219 1-1/64 1.0156 1-1/32 1.0313
12 .8978 15/16 .9375 61/64 .9531
20 .9387 61/64 .9531 31/32 .9688
1-1/16 1.0625 18 .9943 1.000 1.000 1-1/64 1.0156 1-5/64 1.0781 1-3/32 1.0938
1- 1.1250 7 .9497 63/64 .9844 1-1/32 1.0313 1-9/64 1.1406 1-5/32 1.1562
12 1.0228 1-3/64 1.0469 1-5/64 1.0781
18 1.0568 1-1/16 1.0625 1-5/64 1.0781
1-3/16 1.1875 18 1.1193 1-⅛ 1.1250 1-9/64 1.1406 1-13/64 1.2031 1-7/32 1.2188

1-¼

1.2500

7 1.0747 1-7/64 1.1094 1-5/32 1.1562

1-17/64

1.2656

1-9/32

1.2812

12 1.1478 1-11/64 1.1719 1-13/64 1.2031
18 1.1818 1-3/16 1.1875 1-13/64 1.2031
1-5/16 1.3125 18 1.2443 1-¼ 1.2500 1-17/64 1.2656 1-21/64 1.3281 1-11/32 1.3438
1- 1.3750 6 1.1705 1-7/32 1.2187 1-17/64 1.2656 1-25/64 1.3906 1-13/32 1.4062
12 1.2728 1-19/64 1.2969 1-21/64 1.3281
18 1.3068 1-5/16 1.3125 1-21/64 1.3281
1-7/16 1.4375 18 1.3693 1- 1.3750 1-25/64 1.3906 1-29/64 1.4531 1-15/32 1.4688
1-½ 1.500 6 1.2955 1-11/32 1.3437 1-25/64 1.3906 1-33/64 1.5156 1-17/32 1.5312
12 1.3978 1-27/64 1.4219 1-7/16 1.4375
18 1.4318 1-7/16 1.4375 1-29/64 1.4531
1-9/16 1.5625 18 1.4943 1-½ 1.500 1-33/64 1.5156 1-37/64 1.5781 1-19/32 1.5938
1- 1.625 18 1.5568 1-9/16 1.5625 1-37/64 1.5781 1-41/64 1.6406 1-21/32 1.6562
1-11/16 1.6875 18 1.6193 1- 1.6250 1-41/64 1.6406 1-45/64 1.7031 1-23/32 1.7188
1-¾ 1.750 5 1.5046 1-9/16 1.5625 1- 1.6250 1-49/64 1.7659 1-25/32 1.7812

Metric Tap Drill Chart

Metric
Tap
Size
Major
Diameter (mm)
mm/thread (peak to peak) Tap Drill
(mm)
Tap
Drill
(inch)
Clearance
(mm)
Clearance
(inch)
 M 1.6 x 0.35 1.6 0.35 1.25 #55 1.8 #49
 M 2 x 0.4 2 0.4 1.6 #52 2.4 #41
 M 2.5 x 0.45 2.5 0.45 2.05 #46 2.9 #32
 M 3 x .05 3 0.5 2.5 #39 3.4 #29
 M 3.5 x 0.6 3.5 0.6 2.9 #32 3.9 #23
 M 4 x 0.7 4 0.7 3.3 #30 4.5 #16
 M 5 x 0.8 5 0.8 4.2 #19 5.5 7/32
 M 6 x 1 6 1 5 #8 6.6 G
 M 8 x 1.25 8 1.25 6.8 H 9 T
 M 8 x 1 8 1 7 J 9 T
 M 10 x 1.5 10 1.5 8.5 R 12 31/64
 M 10 x 1.25 10 1.25 8.8 11/32 12 31/64
 M 12 x 1.75 12 1.75 10.2 13/32 14 35/64
 M 12 x 1.25 12 1.25 10.8 27/64 14 35/64
 M 14 x 2 14 2 12 15/32 16
 M 14 x 1.5 14 1.5 12.5 ½ 16
 M 16 x 2 16 2 14 35/64 18 45/64
 M 16 x 1.5 16 1.5 14.5 37/64 18 45/64
 M 18 x 2.5 18 2.5 15.5 39/64 20 51/64
 M 18 x 1.5 18 1.5 16.5 21/32 20 51/64
 M 20 x 2.5 20 2.5 17.5 11/16 22
 M 20 x 1.5 20 1.5 18.5 47/64 22
 M 22 x 2.5 22 2.5 19.5 49/64 25 1
 M 22 x 1.5 22 1.5 20.5 13/16 25 1
 M 24 x 3 24 3 21 53/64 27 1-5/64
 M 24 x 2 24 2 22 27 1-5/64
 M 27 x 3 27 3 24 15/16 30 1-3/16

 M 27 x 2

27 2 25 1 30 1-3/16

Pipe Threads
 

  American Standard British Standard
Nominal OD Threads/inch NPT NPS Threads/inch Drill size
1/16 27 D ¼ 28 G
27 R S 28 11/32
¼ 18 7/16 29/64 19 15/32
18 37/64 19/32 19 39/64
½ 14 23/32 47/64 14 ¾
- - - 14 53/64
¾ 14 59/64 15/16 14 31/32
- - - 14 1-7/64
1 11.5 1-5/32 1-3/16 11 1-7/32

Sheet Metal

Sheet Metal Screw Size Thread Diameter Pilot Hole Drill Size
#4

.11

7/64

.09

3/32

#6

.14

9/64

.11

7/64

#8

.17

11/64

.125

1/8

#10

.19

3/16

.14

9/64

#12

.22

7/32

.16

5/32

#14

.25

1/4

.19

3/16

5/16”

---

---

.25

1/4


Thread diameter.

Drilled holes are for clearance. The resulting hole size is often larger than the drill & may not be perfectly round.
 Precision holes are either reamed or bored.