Machine screw size chart

Every numbered and fractional machine screw from #0-80 to 1/2"-20, with head sizes, tap drills and clearance holes.

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Unified inch · ASME B1.1

#10-24UNC

0.190" / 4.83 mm major diameter

Tap drill · 75%

#25

0.149" · 3.8 mm

74.8% thread

Hardware-store bit

5/32"

0.1563"

62.4% thread

Wrench / hex key

3/8"nut5/32"Allen

Drills & threading

Major diameter: 0.190"4.83 mm · nearest 3/16"
Pitch: 24 TPI UNC0.0417" · 1.058 mm
Tap drill 75%: #25 · 74.8%0.1495" · 3.8 mm
Hardware-store bit: 5/32" · 62.4%0.1563" from a 1/64" set
Form / roll tap 65%: 11/64"0.1719" · 4.37 mm
STI / Helicoil: 13/64"#10-24 STI tap · 0.2031"
Clearance · close / free: #9 / #70.1960" / 0.2010"
Counterbore: 3/8"0.375" · 9.52 mm

Wrenches, keys & torque

Hex head: 5/16"head 0.120" · 3.05 mm tall
Nut: 3/8"0.125" · 3.17 mm thick · flange OD N/A
Socket cap key: 5/32"head ⌀ 0.312" · 7.92 mm
Button / flat · set: 1/8" · 3/32"
Flat washer SAE: 0.219" / 0.5"No USS washer at this size
SAE Gr 2 · Gr 5: 27 in-lb · N/A
SAE Grade 8: N/ASAE J429 grades start at 1/4"
18-8 stainless: 32 in-lbGalling risk: use anti-seize on stainless and tighten slowly.

Full chart 29 rows

Sort any column, filter by series, print a shop sheet. Click a row to load it on the gauge.

Machine screw size chart (#0 to 1/2")

29 rows

Machine screw size chart (#0 to 1/2") · ScrewBoltChart

screwboltchart.com · inch-first · tap drills 75% (soft metals) · torque dry, K=0.20 · verify against the governing standard


UNF	80 TPI	0.060" · 1.52 mm	0.116"	0.119"	5/32"	3/64" (80.7%)	#52 (0.0635")	#50 (0.0700")
UNC	64 TPI	0.073" · 1.85 mm	0.142"	0.146"	5/32"	#53 (66.5%)	#48 (0.0760")	#46 (0.0810")
UNF	72 TPI	0.073" · 1.85 mm	0.142"	0.146"	5/32"	#53 (74.8%)	#48 (0.0760")	#46 (0.0810")
UNC	56 TPI	0.086" · 2.18 mm	0.167"	0.172"	3/16"	#50 (69%)	#43 (0.0890")	#41 (0.0960")
UNF	64 TPI	0.086" · 2.18 mm	0.167"	0.172"	3/16"	#50 (78.8%)	#43 (0.0890")	#41 (0.0960")
UNC	48 TPI	0.099" · 2.51 mm	0.193"	0.199"	3/16"	#47 (75.7%)	#37 (0.1040")	#35 (0.1100")
UNF	56 TPI	0.099" · 2.51 mm	0.193"	0.199"	3/16"	#45 (73.3%)	#37 (0.1040")	#35 (0.1100")
UNC	40 TPI	0.112" · 2.84 mm	0.219"	0.225"	1/4"	#43 (70.8%)	#32 (0.1160")	#30 (0.1285")
UNF	48 TPI	0.112" · 2.84 mm	0.219"	0.225"	1/4"	#42 (68.4%)	#32 (0.1160")	#30 (0.1285")
UNC	40 TPI	0.125" · 3.18 mm	0.245"	0.252"	5/16"	#38 (72.4%)	#30 (0.1285")	#29 (0.1360")
UNF	44 TPI	0.125" · 3.18 mm	0.245"	0.252"	5/16"	#37 (71.1%)	#30 (0.1285")	#29 (0.1360")
UNC	32 TPI	0.138" · 3.51 mm	0.270"	0.279"	5/16"	#36 (77.6%)	#27 (0.1440")	#25 (0.1495")
UNF	40 TPI	0.138" · 3.51 mm	0.270"	0.279"	5/16"	#33 (77%)	#27 (0.1440")	#25 (0.1495")
UNC	32 TPI	0.164" · 4.17 mm	0.322"	0.332"	11/32"	#29 (69%)	#18 (0.1695")	#16 (0.1770")
UNF	36 TPI	0.164" · 4.17 mm	0.322"	0.332"	11/32"	#29 (77.6%)	#18 (0.1695")	#16 (0.1770")
UNC	24 TPI	0.190" · 4.83 mm	0.373"	0.385"	3/8"	#25 (74.8%)	#9 (0.1960")	#7 (0.2010")
UNF	32 TPI	0.190" · 4.83 mm	0.373"	0.385"	3/8"	#21 (76.4%)	#9 (0.1960")	#7 (0.2010")
UNC	24 TPI	0.216" · 5.49 mm	0.425"	0.438"	7/16"	#16 (72.1%)	#2 (0.2210")	#1 (0.2280")
UNF	28 TPI	0.216" · 5.49 mm	0.425"	0.438"	7/16"	#14 (73.3%)	#2 (0.2210")	#1 (0.2280")
UNC	20 TPI	0.250" · 6.35 mm	0.492"	0.507"	7/16"	#7 (75.4%)	F (0.2570")	H (0.2660")
UNF	28 TPI	0.250" · 6.35 mm	0.492"	0.507"	7/16"	#3 (79.8%)	F (0.2570")	H (0.2660")
UNC	18 TPI	0.313" · 7.94 mm	0.615"	0.635"	1/2"	F (76.9%)	P (0.3230")	Q (0.3320")
UNF	24 TPI	0.313" · 7.94 mm	0.615"	0.635"	1/2"	I (74.8%)	P (0.3230")	Q (0.3320")
UNC	16 TPI	0.375" · 9.52 mm	0.740"	0.762"	9/16"	5/16" (77%)	W (0.3860")	X (0.3970")
UNF	24 TPI	0.375" · 9.52 mm	0.740"	0.762"	9/16"	Q (79.4%)	W (0.3860")	X (0.3970")
UNC	14 TPI	0.437" · 11.11 mm	N/A	0.812"	11/16"	U (74.9%)	29/64" (0.4531")	15/32" (0.4688")
UNF	20 TPI	0.437" · 11.11 mm	N/A	0.812"	11/16"	25/64" (72.2%)	29/64" (0.4531")	15/32" (0.4688")
UNC	13 TPI	0.500" · 12.7 mm	N/A	0.875"	3/4"	27/64" (78.2%)	33/64" (0.5156")	17/32" (0.5313")
UNF	20 TPI	0.500" · 12.7 mm	N/A	0.875"	3/4"	29/64" (72.2%)	33/64" (0.5156")	17/32" (0.5313")

05 / Field guide

The numbered
screws, decoded.

Machine screws below 1/4" are sized by gauge number, from #0 up to #12. They hold electronics, hardware, panels and small mechanisms, and almost all the confusion around them comes from the numbers.

What the numbers mean

The gauge is an index, not a measurement: #0 is 0.060" and each step adds 0.013". The second number is the thread count. A #6-32 is 0.138" with 32 threads per inch; a #10-24 is 0.190" with 24. #5 and #12 exist but are hard to find, and #7, #9 and #11 are not machine-screw sizes at all.

major diameter (in) = 0.060 + 0.013 × N

Head styles and where length is measured

Pan, hex, socket, button and truss heads are measured from under the head to the tip. Flat (countersunk) heads are measured overall, because the head sits flush in the part. Oval heads are measured from the countersink edge. That is why the caliper above moves the zero line when you change head style.

Thread percentage, in one line

Thread percentage is how much of the full thread depth the tap actually cuts. 100% sounds ideal, but a 75% thread is only about 5% weaker in a steel nut and takes roughly a third of the torque to tap. That is why every tap chart is built around 75%.

% thread = (major diameter − drill) × 76.98 × TPI metric: (D − drill) × 76.98 ÷ P

Hardware-store bits for small taps

Below 1/4" the 1/64" steps of a fractional set are coarse compared with the thread depth, so the nearest bit often lands far from 75%. A 9/64" bit in an #8-32 gives about 58% thread; a 7/64" in a #6-32 gives about 71%. For #2 and #3 screws a fractional bit is either too small to clear the tap or too large to leave a thread, so buy the number drill. The chart flags every weak combination.

Questions

Answered plainly.

01What is the most common machine screw size?+

In North American hardware, #6-32, #8-32 and #10-24 cover most needs. #4-40 is common in electronics, and #10-32 is the go-to fine thread for instruments and optical mounts.

02What drill do I use for a #6-32 tap?+

A #36 drill (0.1065") gives about 78% thread. From a fractional set, a 7/64" bit gives about 71%, which is perfectly usable. The clearance hole is #27 for a close fit or #25 for a free fit.

03What is the difference between 10-24 and 10-32?+

Both are 0.190" in diameter. 10-24 is the coarse thread (UNC) and 10-32 the fine one (UNF). They are not interchangeable: a 10-32 screw will not start in a 10-24 hole. 10-24 needs a #25 tap drill and 10-32 a #21.

04What size nut driver fits a #8 nut?+

A standard #8 machine-screw hex nut is 11/32" across flats. A #6 nut is 5/16" and a #10 nut is 3/8".

05Why is my #4-40 tap breaking?+

Small taps break when the hole is too small or chips pack the flutes. Use a #43 drill (about 71% thread), back the tap out half a turn every turn, and use cutting oil. In stainless, step up to a 3/32" drill for a lighter 56% thread.

06Are #12 screws standard?+

#12-24 and #12-28 are standard UN threads, but #12 socket head cap screws are not part of ASME B18.3, so socket and key dimensions are marked N/A for that size.

07What clearance hole for a #10 screw?+

A #9 drill (0.196") for a close fit or a #7 (0.201") for a free fit. Use the free fit when several holes have to line up.