Tapping Threads & Associated Reference Tables
Last updated on Tuesday, April 08, 2014 06:32:58 AM Eastern US Time Zone

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Tables, Hand Tappers, Tap Handles, Cutting Fluids, Tap Guides, Tapmatic 30XDie Holders,
Drill-Tap Sets, Drill-Tap Chart, Thread Measurement, Bolt Head Grade Identification, Bolt Torque

Introduction to Taps   Single-point threading Section   How to Drill a Hole   Hand Tapper Manual   Machinist Calculator

Tables
National Unified Coarse & Fine Thread Dimensions with Tap Drill Sizes   Standard Acme Screw Thread Dimensions
ISO External Threads   Double Depth of Screw Threads   Standard Pipe Thread & Tap Drill Sizes
Tap Drill Sizes for Fractional Size Threads   mm Tap Drill Sizes   Decimal Equivalents of Number Size Drills
Metric & Inch Equivalents   Decimal Equivalents of Fractions   Inch to mm Conversion   mm to Inch Conversion
  Decimal Equivalents of Letter Size Drills   Guide for Cutting Speeds & Feeds for Drills  

Hand Tappers

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.
This hand tapper
includes a set of adapters: #6, #8, #10,
", 5/16", ", 7/16", " & ".
The tap is first fixed to the adapter & then snapped into the spindle.
The handle has two different lengths to modulate the hand torque & it can be easily
removed as it is held in by a tapered pin. For small taps the knurled finger knob is used.
The adjustable counter-weight applies a slight upward force that aids unthreading the tap.
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.

HAND TAPPER SPECIFICATIONS
Tap Capacity #6 to "
Table to Bracket 7"
Spindle to Bracket 7
Table 6 x 12
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 -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 " 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 tap hole tables.
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 percentage threads or use the
Machinist Calculator.


The set of hand tapper adapters: The leftmost is a custom made, aluminum adapter for a ⅛-27 NPT tap.
Then left to right are ⅝", ", ⅜" (2), 7/16", 5/16" (2), ", #10, #8, & #6 hardened steel tap adapters.




Each adapter has a round hole with a setscrew to hold the tap in &
a square hole at the end that positively engages the tap in order 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 5/16-18.
Each hex-shaped adapter has a square hole & a setscrew to securely engage & hold the tap shank.
The shaft rotates in a pressed-in, reamed 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 finger knob is used with smaller taps to allow better feel & lower torque thus reducing chances of breakage.
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 threads into a brass weight.


Tapping 2-56 threads into the end of a brass rod.

Tap Handles

Differently sized tap handles correspond to various tap-size ranges.
Top: The two larger handles are Craftsman (USA).
Middle: The one medium-sized handle is from Germany.
Bottom: The two smaller Starrett (USA) handles have superior design & quality.

The Starrett tap handles have smooth, ideal shapes.

 






Large handle is being used to tap 75% ⅜-16 threads in aluminum.
The smaller blue vise holds the part for transfer to different machining setups.


Maximum chuck capacity is 0.502". This larger tap handle holds up to the 1-1/16" H hand reamer.

Cutting Fluids

Always use the appropriate cutting fluid. Some fluids are specific (e.g., for aluminum) while others generic.
Kerosene works very well for aluminum.


Micro-tap handles for very small (#0 to #6 & M1.6 to M3.5) sizes. Affords good feel while cutting threads.


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


A large, chrome-plated ratchet-type (CW, lock, CCW) tap wrench with a capacity of " ~ " (M6 ~ M14).
The two handles slide out for added leverage & slide in (or to one side) allowing use in tight places.


This tap handle holds up to the " E hand reamer.


Tap handles with sturdy integral end guides (USA).
Top left to right: " to " & " to ". Bottom: 0 to ".


6-32 drilled & tapped (50% threads for steel) in the 9x20 lathe cross slide table back end.
This particular tap handle worked nicely as it has a guide that is mounted into the drill press chuck.
The large steel cross slide is 9-inches long. Everything is securely clamped & the table is locked.


Drilling a 7/32" hole in the end of a 0.79" x 19.7" (20mm x 500mm) steel rod in preparation for a -20 thread.
The long rod passes through the hole & hangs below the table surface of the large floor drill press.

Smaller tap wrench.
 

Larger tap wrench.
 


The lowest speed can usually keep the chuck from turning but sometimes I use a Tommy bar in the chuck.

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 & tapping range.


Wooden tap wrench holder.

 



A Yankee No. 251 (North Bros Mfg, Co., Philadelphia, PA, USA) ratcheting tap wrench that has a brass body.

Tap Guides

Shop fabricated steel (left) & aluminum (right) guides help start perpendicular tapping in difficult locations.
The series of holes match the US standard tap shank diameters. The smaller holes are for select drill bit sizes.
 


Clamping when possible helps.


Holes are threaded with a 6-32 tap for a Taig mill DRO modification.
 


 


 


Steel tap guides for both standard & metric sizes (USA). Some smaller guide holes would be useful.

 


The bottom is precision ground & has a V-groove to allow accurate centering when tapping round parts.


 

Self-aligning tap & reamer fixture (China). Jaws needed deburring. Variable quality; not recommended.
Useful for making tapped holes outside of the controlled environment of the workshop.

 


 

Supplied with two sets (small & large) hardened jaws to accommodate a 0-80 to -13 tap size range.
The handle is too large for small taps & too small for large taps unless the material is soft, e.g., Delrin.

 



The base has two, 120 Vees for centering on round stock.

 


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


This photo shows how each tip type is used for the spring-loaded guide.

Tapmatic 30X

The Tapmatic 30X is expensive but can be found on the net for a good price, used.
It requires a torque bar attached to either the table or the quill. Fabrication details are shown, below.
Handy device if many holes need to be tapped using the mill. Tapmatic 30X instructions.



 



Milling a 3.6" hole on the rotary table.


Tapping an 8-32 thread on one side of the slot followed by drilling a clearance hole on the other side.

 


Milling a slot for the quill clamp.

 


The torque bar is a ⅜" steel rod fastened by a 10-32 bolt with a washer.

 

Die Holders

Die handles: Top one (India) is for 1" diameter dies (a split-type is shown), next one is for hex-style dies.
The hex die-to-tap adapter is from the metric set. One-inch (GER) & 13/16" (USA) round-die holders shown.



Small dies & taps (left to right): 0-80, 1-72, M2-0.4 (in 13/16" die handle) 2-56, 3-48. Small red tap handle.
 


Wooden tap stand being made using the CNC mill.
 


0-80, 1-64, 1-72, 2-56, 3-48, 4-36, 4-40, 4-48, 5-40, 6-32 taps.

 


A handle that holds 20mm dies. An M6-1 left-hand die is shown.

 


Metric die & tap set (USA).


1" & 13/16" round die holder slides on a 9/16" steel rod with an MT2 adapter for the 9x20 lathe tailstock.
Refer to Machinery's Handbook for the proper major diameter dimensions for any given threaded rod.


The body is knurled for good grip & the removable steel bar can be added for more leverage.
Hand use without the bar gives good, low-torque control for threading delicate parts.


This is a hex & round (two sizes) die holder. The pockets were CNC fabricated




Die holders for threading while the part is on the lathe. The top holder is for 1.5" dies.

Drill-Tap Sets

Left to right: examples of tapered, plug & bottoming taps. -20 size shown.

Drill & taper tap sets (18 pieces each) left to right: metric, National Fine (NF) & National Coarse (NC).
Metric: M2.5-.45, M3-.5, M3.5-.6, M4-.7, M5-.8, M6-1, M8-1.25, M10-1.5, & M12-1.75.

NF:  6-40, 8-36, 10-24, 10-32, -28, 5/16-24, ⅜-24, 7/16-20, & -20.

NC:  6-32, 8-32, 10-24, 10-32, -20, 5/16-18, ⅜-16, 7/16-14, & -13.

Note: the drill bit sizes are for 75% threads in aluminum, brass & plastic.


 

 

Plug & bottom tap sets (USA). The spiral flutes are effective in removing swarf, especially from blind holes.

 


Spiral flutes effectively remove swarf.


HSS combination drill bit & tap. Imperial sizes: 4-40, 6-32, 8-32, 10-32, 10-24, -28, -20, 5/16-18, ⅜-16 &
-13.


Combination drill bit, tap, & deburr/countersink. Metric sizes: M3x.5, M4x.7, M5x.8, M6x1, M8x1.25, & M10x1.5
Each HSS bit has an integral deburr/countersink & quick-change hex shaft.
Note the taper after the threading that prevents over drilling.


Imperial sizes: 6-32, 8-32, 10-24, 10-32, 12-24 & -20
. Variable quality in an import.

Unified Tap Drill Chart: Tap drill bit references for imperial, metric, & pipe threads.   Additional tap-drill charts.

MACHINE
 SCREW SIZE
NUMBER of THREADS/IN. MINOR DIAMETER TAP DRILLS CLEARANCE HOLE DRILLS
Aluminum, Brass & Plastic
75% Thread
Stainless Steel, Steel & 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
.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
.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

.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 1⅛ 1.1250 1-9/64 1.1406 1-13/64 1.2031 1-7/32 1.2188

1

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 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 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 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 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
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 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

 
SHEET METAL
SHEET METAL
SCREW SIZE
THREAD
 DIAMETER (inch)
PILOT HOLE
 DRILL SIZE (inch)
#4 .11 7/64 .09 3/32
#6 .14 9/64 .11 7/64
#8 .17 11/64 .125
#10 .19 3/16 .14 9/64
#12 .22 7/32 .16 5/32
#14 .25 .19 3/16
5/16 --- --- .25



Thread diameter.
 

PIPE THREAD
  AMERICAN STANDARD BRITISH STANDARD
Nominal OD Threads/inch NPT NPS Threads/inch Drill size
1/16 27 D 28 G
27 R S 28 11/32
18 7/16 29/64 19 15/32
18 37/64 19/32 19 39/64
14 23/32 47/64 14
- - - 14 53/64
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

Taper pipe thread tapping requires greater accuracy & it subjects the tools to higher stresses.
Pipe threads must be formed more accurately, because 100% of the thread height must be cut by
the tap or other pipe-threading tool to maintain the standard thread profile. A machinist looking at a
-14 pipe tap is likely to note that the tap diameter is larger than ". In fact, the tap's diameter at
the large end is 0.865". The tap's designation refers to the inner diameter (ID) of the standard iron
pipe it is designed to thread. Therefore, a -14 taper pipe thread tap is designed to tap a " ID
pipe. The external thread on a pipe with a " ID is at least the size of the ID plus the amount of
two wall thicknesses. To achieve the basic thread depth, drive the tap into the work piece 12 turns.

 

ISO METRIC TRAPEZOIDAL THREADS
EXTERNAL (Class 7E)
  Major Diameter Pitch Diameter Minor Diameter
Size (mm) Thread Designation Pitch (mm) Max Min Max Min Max Min
8 TR 8x1.5 1.5 8 7.85 7.183 7.013 6.2 5.921
9 TR 9X1.5 1.5 9 8.85 8.183 8.013 7.2 6.921
9 TR 9X2 2 9 8.82 7.929 7.739 6.5 6.191
10 TR 10X1.5 1.5 10 9.85 9.183 9.013 8.2 7.921
10 TR 10X2 2 10 9.82 8.929 8.739 7.5 7.191
11 TR 11X2 2 11 10.82 9.929 9.739 8.5 8.191
11 TR 11X3 3 11 10.764 9.415 9.203 7.5 7.15
12 TR 12X2 2 12 11.82 10.929 10.729 9.5 9.179
12 TR 12X3 3 12 11.764 10.415 10.191 8.5 8.135
14 TR 14X2 2 14 13.82 12.929 12.729 11.5 11.179
14 TR 14X3 3 14 13.764 12.415 12.191 10.5 10.135
16 TR 16X2 2 16 15.82 14.929 14.729 13.5 13.179
16 TR 16X3 3 16 15.764 14.415 14.191 12.5 12.135
16 TR 16X4 4 16 15.7 13.905 13.64 11.5 11.074
18 TR 18X2 2 18 17.82 16.929 16.729 15.5 15.179
18 TR 18X3 3 18 17.764 16.415 16.191 14.5 14.135
18 TR 18X4 4 18 17.7 15.905 15.64 13.5 13.074

Trapezoidal (metric) screw thread has a 30 included angle. ACME screw thread has a 29 included angle.
Trapezoidal screw thread is made & measured in millimeters. ACME screw thread is made & measured in inches.
Trapezoidal screw thread pitch is stated in millimeters of pitch. ACME screw thread pitch is stated in threads per inch.

ISO METRIC TRAPEZOIDAL THREADS
INTERNAL (Class 7H)
  Minor Diameter Pitch Diameter Major Diameter
Size (mm) Thread Designation Pitch (mm) Min Max Min Max Min
8 TR 8x1.5 1.5 6.5 6.69 7.25 7.474 8.3
9 TR 9X1.5 1.5 7.5 7.69 8.25 8.474 9.3
9 TR 9X2 2 7 7.236 8 8.25 9.5
10 TR 10X1.5 1.5 8.5 8.69 9.25 9.474 10.3
10 TR 10X2 2 8 8.236 9 9.25 10.5
11 TR 11X2 2 9 9.236 10 10.25 11.5
11 TR 11X3 3 8 8.315 9.5 9.78 11.5
12 TR 12X2 2 10 10.236 11 11.265 12.5
12 TR 12X3 3 9 9.315 10.5 10.8 12.5
14 TR 14X2 2 12 12.236 13 13.265 14.5
14 TR 14X3 3 11 11.315 12.5 12.8 14.5
16 TR 16X2 2 14 14.236 15 15.265 16.5
16 TR 16X3 3 13 13.315 14.5 14.8 16.5
16 TR 16X4 4 12 12.375 14 14.355 16.5
18 TR 18X2 2 16 16.236 17 17.265 18.5
18 TR 18X3 3 15 15.315 16.5 16.8 18.5
18 TR 18X4 4 14 14.375 16 16.355 18.5

Formula for tap drill bit (round to closest available drill bit size): D1+(0.05 * p). Where: D1 = minimum internal thread minor diameter, p = pitch
 

STANDARD ACME THREAD PITCHES

NOMINAL DIAMETER (in)

PITCH (in)

1/16

5/16

1/14

1/12
1/10

1/6

1, 1 1/5
1, 1, 2
2

1/3

3

Thread Measurement

Screw thread micrometer with five different anvil pairs to measure both unified &
metric external pitch diameter. 0" to 1" measurement range with a 0.0001" scale.

SCREW THREAD MICROMETER ANVILS

ANVIL #

1

2

3

4

5

TPI RANGE

64 - 48

44 - 28

24 - 14

13 - 9

8 - 5

 METRIC RANGE

0.4 - 0.5

0.6 - 0.9

1 - 1.75

2 - 3

3.5 - 5


Anvil pairs are clearly marked for pitch range.


Example measurement of a -20 screw. The micrometer reading is 0.2160". Table pitch value is 0.2164" max.
A fast & accurate thread measurement tool. The bolt can freely rotate around the micrometer's anvil axis.


Standard Unified & metric thread gages.


29 ACME (1n - 12n) & 30 ISO (2p - 20p) thread gages.

BOLT HEAD GRADE IDENTIFICATION MARKINGS - ASTM & SAE Standards
Grade Marking Specification Material Bolt & Screw Size Proof Load
PSI
Tensile Strength
MINIMUM PSI
SAE - Grade 1  Low Carbon Steel  " - 1 33,000 60,000
ASTM - A307 Low Carbon Steel  " -
 1
" - 4"  
33,000 60,000
 55,000 
SAE - Grade 2  Low Carbon Steel  " - "
 " - 1
55,000
 33,000 
74,000
 60,000 
SAE - Grade 3  Medium Carbon Steel
Cold Worked  
" - 1"
 
" -
85,000
 80,000 
110,000
 100,000 
SAE - Grade 5
ASTM - A449 
Medium Carbon Steel,
Quenched & Tempered 
 " - 1"
Over 1" - 1
"
 Over 1
" - 3" 
85,000
74,000
 55,000 
120,000
105,000
  90,000
ASTM - A325  Medium Carbon Steel,
Quenched & Tempered 
", ", "
", 1"
 1" - 1
85,000
78,000
 74,000 
120,000
115,000
 105,000 
ASTM - A354
Grade BB 
Low Alloy Steel,
Quenched & Tempered 
" - 2"
 Over 2
" - 4" 
80,000
 75,000 
105,000
 100,000 
ASTM - A354
Grade BC
Low Alloy Steel,
Quenched & Tempered 
" - 2"
 Over 2
" - 4" 
105,000
   95,000 
125,000
 115,000 
SAE - Grade 5.1 Low or Medium Carbon 
Steel, Quenched & Tempered, with Assembled Lock Washer 
Up to " incl. 85,000 120,000
SAE - Grade 7
Medium Carbon Alloy Steel, Quenched & Tempered,
Roll Threaded
after Heat Treatment 
" - 1" 105,000 133,000
SAE - Grade 8 Medium Carbon
Alloy Steel, 
Quenched & Tempered 
" - 1" 120,000 150,000
ASTM - A354
Grade BD 
Alloy Steel,
Quenched & Tempered 
" - 1" 120,000 150,000
ASTM - A490 Alloy Steel,
Quenched & Tempered 
" - 2"
 Over 2
" - 4" 
120,000
 105,000 
150,000
 140,000 


I buy metal hardware for 1USD per lb., at a local surplus store. It takes over 440 bins to keep it all sorted.


The newer polypropylene plastic drawers are much stronger & won't crack/break like the clear ones.

Bolt Torque
Torque is the tendency of a force to rotate an object about an axis, fulcrum, or pivot.  

A torque screwdriver set to 20 in-lbs.


Torque ranges are specified for different screw & bolt types. Torque screwdriver instructions
It varies as a function of size, material, number of threads, hardness, plating, lubrication, etc.
There are numerous torque reference tables available on the web; it's common to over-torque.
 Store torque wrenches at the lowest setting to help maintain long-term accuracy.


Selecting a bit that fits a given screw greatly reduces damage. Gunsmithing screwdriver set


", ⅜", & " drive torque wrenches. Store torque wrenches at the lowest setting to help maintain accuracy.
The (top) 3 wrenches measure ft-lbs (Newton-meters); the (bottom) " drive wrench measures in-lbs (cm-kgs).

Tables, Hand Tappers, Tap Handles, Cutting Fluids, Tap Guides, Tapmatic 30XDie Holders,
Drill-Tap Sets, Drill-Tap Chart, Thread Measurement, Bolt Head Grade Identification, Bolt Torque

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