Screw size chart & 1:1 fastener sizer

Lay a screw on your screen to identify it at true size, or type any size, measurement, drill or wrench to get every spec in one card.

Reading your screen…

Unified inch · ASME B1.1

#8-32UNC

0.164" / 4.17 mm major diameter

Tap drill · 75%

#29

0.136" · 3.45 mm

69% thread

Hardware-store bit

9/64"

0.1406"

57.6% thread

Wrench / hex key

11/32"nut9/64"Allen

Drills & threading

Major diameter: 0.164"4.17 mm · nearest 5/32"
Pitch: 32 TPI UNC0.0313" · 0.794 mm
Tap drill 75%: #29 · 69%0.1360" · 3.45 mm
Hardware-store bit: 9/64" · 57.6%Weak thread: use the numbered drill if possible
Form / roll tap 65%: #250.1495" · 3.8 mm
STI / Helicoil: #17#8-32 STI tap · 0.1730"
Clearance · close / free: #18 / #160.1695" / 0.1770"
Counterbore: 5/16"0.313" · 7.94 mm

Wrenches, keys & torque

Hex head: 1/4"head 0.110" · 2.79 mm tall
Nut: 11/32"0.125" · 3.17 mm thick · flange OD N/A
Socket cap key: 9/64"head ⌀ 0.270" · 6.86 mm
Button / flat · set: 3/32" · 5/64"
Flat washer SAE: 0.188" / 0.438"No USS washer at this size
SAE Gr 2 · Gr 5: 19 in-lb · N/A
SAE Grade 8: N/ASAE J429 grades start at 1/4"
18-8 stainless: 22 in-lbGalling risk: use anti-seize on stainless and tighten slowly.

Full chart 70 rows

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

Screw size chart (US & metric)

70 rows

Screw size chart (US & metric) · 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	1/16"	3/64" (80.7%)	#52 (0.0635")	0.050"
UNC	64 TPI	0.073" · 1.85 mm	5/64"	#53 (66.5%)	#48 (0.0760")	1/16"
UNF	72 TPI	0.073" · 1.85 mm	5/64"	#53 (74.8%)	#48 (0.0760")	1/16"
UNC	56 TPI	0.086" · 2.18 mm	3/32"	#50 (69%)	#43 (0.0890")	5/64"
UNF	64 TPI	0.086" · 2.18 mm	3/32"	#50 (78.8%)	#43 (0.0890")	5/64"
UNC	48 TPI	0.099" · 2.51 mm	3/32"	#47 (75.7%)	#37 (0.1040")	5/64"
UNF	56 TPI	0.099" · 2.51 mm	3/32"	#45 (73.3%)	#37 (0.1040")	5/64"
UNC	40 TPI	0.112" · 2.84 mm	7/64"	#43 (70.8%)	#32 (0.1160")	3/32"
UNF	48 TPI	0.112" · 2.84 mm	7/64"	#42 (68.4%)	#32 (0.1160")	3/32"
UNC	40 TPI	0.125" · 3.18 mm	1/8"	#38 (72.4%)	#30 (0.1285")	3/32"
UNF	44 TPI	0.125" · 3.18 mm	1/8"	#37 (71.1%)	#30 (0.1285")	3/32"
UNC	32 TPI	0.138" · 3.51 mm	9/64"	#36 (77.6%)	#27 (0.1440")	7/64"
UNF	40 TPI	0.138" · 3.51 mm	9/64"	#33 (77%)	#27 (0.1440")	7/64"
UNC	32 TPI	0.164" · 4.17 mm	5/32"	#29 (69%)	#18 (0.1695")	9/64"
UNF	36 TPI	0.164" · 4.17 mm	5/32"	#29 (77.6%)	#18 (0.1695")	9/64"
UNC	24 TPI	0.190" · 4.83 mm	3/16"	#25 (74.8%)	#9 (0.1960")	5/32"
UNF	32 TPI	0.190" · 4.83 mm	3/16"	#21 (76.4%)	#9 (0.1960")	5/32"
UNC	24 TPI	0.216" · 5.49 mm	7/32"	#16 (72.1%)	#2 (0.2210")	N/A
UNF	28 TPI	0.216" · 5.49 mm	7/32"	#14 (73.3%)	#2 (0.2210")	N/A
UNC	20 TPI	0.250" · 6.35 mm	1/4"	#7 (75.4%)	F (0.2570")	3/16"
UNF	28 TPI	0.250" · 6.35 mm	1/4"	#3 (79.8%)	F (0.2570")	3/16"
UNC	18 TPI	0.313" · 7.94 mm	5/16"	F (76.9%)	P (0.3230")	1/4"
UNF	24 TPI	0.313" · 7.94 mm	5/16"	I (74.8%)	P (0.3230")	1/4"
UNC	16 TPI	0.375" · 9.52 mm	3/8"	5/16" (77%)	W (0.3860")	5/16"
UNF	24 TPI	0.375" · 9.52 mm	3/8"	Q (79.4%)	W (0.3860")	5/16"
UNC	14 TPI	0.437" · 11.11 mm	7/16"	U (74.9%)	29/64" (0.4531")	3/8"
UNF	20 TPI	0.437" · 11.11 mm	7/16"	25/64" (72.2%)	29/64" (0.4531")	3/8"
UNC	13 TPI	0.500" · 12.7 mm	1/2"	27/64" (78.2%)	33/64" (0.5156")	3/8"
UNF	20 TPI	0.500" · 12.7 mm	1/2"	29/64" (72.2%)	33/64" (0.5156")	3/8"
UNC	12 TPI	0.563" · 14.29 mm	9/16"	31/64" (72.1%)	37/64" (0.5781")	N/A
UNF	18 TPI	0.563" · 14.29 mm	9/16"	33/64" (65%)	37/64" (0.5781")	N/A
UNC	11 TPI	0.625" · 15.88 mm	5/8"	17/32" (79.3%)	41/64" (0.6406")	1/2"
UNF	18 TPI	0.625" · 15.88 mm	5/8"	37/64" (65%)	41/64" (0.6406")	1/2"
UNC	10 TPI	0.750" · 19.05 mm	3/4"	21/32" (72.1%)	49/64" (0.7656")	5/8"
UNF	16 TPI	0.750" · 19.05 mm	3/4"	11/16" (77%)	49/64" (0.7656")	5/8"
UNC	9 TPI	0.875" · 22.23 mm	7/8"	49/64" (75.8%)	57/64" (0.8906")	3/4"
UNF	14 TPI	0.875" · 22.23 mm	7/8"	13/16" (67.4%)	57/64" (0.8906")	3/4"
UNC	8 TPI	1.000" · 25.4 mm	1"	7/8" (77%)	1-1/64" (1.0156")	3/4"
UNF	12 TPI	1.000" · 25.4 mm	1"	59/64" (72.1%)	1-1/64" (1.0156")	3/4"
Coarse	0.35 mm	0.063" · 1.6 mm	≈ #0-80	1.25 mm	1.7 mm	1.5 mm
Coarse	0.4 mm	0.079" · 2 mm	≈ #1-64	1.6 mm	2.2 mm	1.5 mm
Coarse	0.45 mm	0.098" · 2.5 mm	≈ #3-56	2.05 mm	2.7 mm	2 mm
Coarse	0.5 mm	0.118" · 3 mm	≈ #4-48	2.5 mm	3.2 mm	2.5 mm
Coarse	0.6 mm	0.138" · 3.5 mm	≈ #6-40	2.9 mm	3.7 mm	2.5 mm
Coarse	0.7 mm	0.157" · 4 mm	≈ #8-36	3.3 mm	4.3 mm	3 mm
Fine	0.5 mm	0.157" · 4 mm	≈ #8-36	3.5 mm	4.3 mm	3 mm
Coarse	0.8 mm	0.197" · 5 mm	≈ #10-32	4.2 mm	5.3 mm	4 mm
Fine	0.5 mm	0.197" · 5 mm	≈ #10-32	4.5 mm	5.3 mm	4 mm
Coarse	1 mm	0.236" · 6 mm	≈ 1/4"-28	5 mm	6.4 mm	5 mm
Fine	0.75 mm	0.236" · 6 mm	≈ 1/4"-28	5.25 mm	6.4 mm	5 mm
Coarse	1.25 mm	0.315" · 8 mm	≈ 5/16"-18	6.8 mm	8.4 mm	6 mm
Fine	1 mm	0.315" · 8 mm	≈ 5/16"-24	7 mm	8.4 mm	6 mm
Coarse	1.5 mm	0.394" · 10 mm	≈ 3/8"-16	8.5 mm	10.5 mm	8 mm
Fine	1.25 mm	0.394" · 10 mm	≈ 3/8"-24	8.8 mm	10.5 mm	8 mm
Fine	1 mm	0.394" · 10 mm	≈ 3/8"-24	9 mm	10.5 mm	8 mm
Coarse	1.75 mm	0.472" · 12 mm	≈ 1/2"-13	10.2 mm	13 mm	10 mm
Fine	1.5 mm	0.472" · 12 mm	≈ 1/2"-20	10.5 mm	13 mm	10 mm
Fine	1.25 mm	0.472" · 12 mm	≈ 1/2"-20	10.8 mm	13 mm	10 mm
Coarse	2 mm	0.551" · 14 mm	≈ 9/16"-12	12 mm	15 mm	12 mm
Fine	1.5 mm	0.551" · 14 mm	≈ 9/16"-18	12.5 mm	15 mm	12 mm
Coarse	2 mm	0.630" · 16 mm	≈ 5/8"-11	14 mm	17 mm	14 mm
Fine	1.5 mm	0.630" · 16 mm	≈ 5/8"-18	14.5 mm	17 mm	14 mm
Coarse	2.5 mm	0.709" · 18 mm	≈ 3/4"-10	15.5 mm	19 mm	14 mm
Fine	1.5 mm	0.709" · 18 mm	≈ 3/4"-16	16.5 mm	19 mm	14 mm
Coarse	2.5 mm	0.787" · 20 mm	≈ 3/4"-10	17.5 mm	21 mm	17 mm
Fine	1.5 mm	0.787" · 20 mm	≈ 3/4"-16	18.5 mm	21 mm	17 mm
Coarse	2.5 mm	0.866" · 22 mm	≈ 7/8"-9	19.5 mm	23 mm	17 mm
Fine	1.5 mm	0.866" · 22 mm	≈ 7/8"-14	20.5 mm	23 mm	17 mm
Coarse	3 mm	0.945" · 24 mm	≈ 1"-8	21 mm	25 mm	19 mm
Fine	2 mm	0.945" · 24 mm	≈ 1"-12	22 mm	25 mm	19 mm

05 / Field guide

How screw sizing
actually works.

Every screw is described by two numbers: how thick it is and how tightly its thread is wound. Get both and the rest of the chart follows: the tap drill, the clearance hole, the wrench and the torque.

Diameter first: gauge, fraction or millimetre

Small inch screws use gauge numbers. A #0 is 0.060" across the threads and each step adds 0.013", so a #8 is 0.164" and a #10 is 0.190". From 1/4" upward the size is simply the fraction. Metric screws state the diameter directly: an M6 is 6 mm across the thread crests.

Real threads are rolled slightly undersize, so calipers usually read 0.05–0.2 mm below the nominal size. A screw that measures 4.8 mm is still a #10 or an M5, never something in between.

gauge diameter (in) = 0.060 + 0.013 × gauge number

Pitch second: TPI or millimetres

Inch threads count threads per inch (TPI). Metric threads give the distance from one crest to the next in millimetres. They are the same idea upside down: 20 TPI is a 1.27 mm pitch.

Diameter alone can’t separate look-alikes. A #10 and an M5 differ by 0.17 mm, less than a pixel on most screens. Their pitches, 24 TPI against 0.8 mm, drift 2.6 mm apart over ten threads, which you can see instantly against the comb.

TPI = 25.4 ÷ pitch (mm)

Coarse or fine

Most sizes come in a coarse series (UNC, metric coarse) and a fine series (UNF, metric fine). Coarse threads assemble faster, tolerate dirt and strip less easily in soft materials. Fine threads are stronger in tension, adjust more precisely and resist vibration loosening. If a screw came out of furniture, a car body or an appliance, it is almost always coarse.

Questions

Answered plainly.

01How do I measure a screw on screen?+

Calibrate once with a coin or a credit card, lay the screw flat on the glass between the jaws and close the upper jaw onto the thread crests. The shortlist shows every size within measuring error; then hold the threads against each pitch comb and pick the one where ten teeth seat with no drift.

02What is the difference between a #8 and a #10 screw?+

A #8 is 0.164" (4.17 mm) across the threads and a #10 is 0.190" (4.83 mm). The #8 usually has 32 threads per inch; the #10 comes in 24 (coarse) or 32 (fine). They take different tap drills (#29 against #25) and different nut wrenches (11/32" against 3/8").

03Is an M5 the same as a #10?+

No. They are within 0.17 mm in diameter but an M5 has a 0.8 mm pitch (about 31.75 TPI) and a #10 has 24 or 32 TPI. Forcing one into the other cross-threads the hole. Use the pitch comb to tell them apart.

04What does #8-32 mean?+

Gauge 8 (0.164" major diameter) with 32 threads per inch. It is the standard coarse thread for a #8 machine screw. Tap it with a #29 drill for a 75% thread, or a 9/64" bit from a hardware-store set for about 58%.

05Should I use the coarse or the fine thread?+

Use coarse unless you have a reason not to. Coarse threads are standard for wood, plastics, aluminium and general assembly. Choose fine threads for thin walls, precise adjustment or high-vibration joints in steel.

06How accurate is the on-screen measurement?+

A coin calibration is good to about ±0.8% and a credit card to about ±0.25%. That is plenty to tell neighbouring sizes apart once you also match the pitch. For critical parts, confirm with a caliper or thread gauge.

07Why does my screen need calibrating?+

Browsers draw in CSS pixels, and how many of those fit in a real inch depends on your screen, its resolution and your display scaling. Matching a coin or card once tells the site your exact pixels per inch, so every outline is drawn at true size.