Enjoy 10% off your first order with code FIRST10 — max $500 discount. Start an Instant Quote

Reference Chart

Bolt & Screw Head Dimensions Chart

Reference chart for bolt and screw head dimensions including socket head cap screws, hex bolts, flat head screws, and button head screws. Covers #4-40 through 3/4-10 (imperial) and M3 through M20 (metric) per ASME B18.3 and ISO 4762.

Fastener Size ▲	Head Diameter (in) ▲	Head Height (in) ▲	Wrench / Drive Size ▲	Thread Length (in) ▲	Type ▲
#4-40	0.183	0.112	3/32" Allen	0.500	Socket Head Cap
#6-32	0.226	0.138	7/64" Allen	0.500	Socket Head Cap
#8-32	0.270	0.164	9/64" Allen	0.625	Socket Head Cap
#10-24	0.312	0.190	5/32" Allen	0.750	Socket Head Cap
1/4"-20	0.375	0.250	3/16" Allen	0.750	Socket Head Cap
5/16"-18	0.469	0.313	1/4" Allen	0.875	Socket Head Cap
3/8"-16	0.563	0.375	5/16" Allen	1.000	Socket Head Cap
1/2"-13	0.750	0.500	3/8" Allen	1.250	Socket Head Cap
5/8"-11	0.938	0.625	1/2" Allen	1.500	Socket Head Cap
3/4"-10	1.125	0.750	5/8" Allen	1.750	Socket Head Cap
M3 x 0.5	5.5 mm	3.0 mm	2.5 mm Allen	12 mm	Socket Head Cap
M4 x 0.7	7.0 mm	4.0 mm	3 mm Allen	14 mm	Socket Head Cap
M5 x 0.8	8.5 mm	5.0 mm	4 mm Allen	16 mm	Socket Head Cap
M6 x 1.0	10.0 mm	6.0 mm	5 mm Allen	18 mm	Socket Head Cap
M8 x 1.25	13.0 mm	8.0 mm	6 mm Allen	22 mm	Socket Head Cap
M10 x 1.5	16.0 mm	10.0 mm	8 mm Allen	26 mm	Socket Head Cap
M12 x 1.75	18.0 mm	12.0 mm	10 mm Allen	30 mm	Socket Head Cap
M16 x 2.0	24.0 mm	16.0 mm	14 mm Allen	38 mm	Socket Head Cap
M20 x 2.5	30.0 mm	20.0 mm	17 mm Allen	46 mm	Socket Head Cap
1/4"-20	0.438 (AF)	0.188	7/16" wrench	0.750	Hex Bolt
5/16"-18	0.500 (AF)	0.235	1/2" wrench	0.875	Hex Bolt
3/8"-16	0.563 (AF)	0.268	9/16" wrench	1.000	Hex Bolt
1/2"-13	0.750 (AF)	0.364	3/4" wrench	1.250	Hex Bolt
5/8"-11	0.938 (AF)	0.444	15/16" wrench	1.500	Hex Bolt
3/4"-10	1.125 (AF)	0.524	1-1/8" wrench	1.750	Hex Bolt
#4-40	0.210	0.065	3/32" Allen	0.500	Flat Head
#6-32	0.262	0.083	7/64" Allen	0.500	Flat Head
#8-32	0.312	0.100	9/64" Allen	0.625	Flat Head
#10-24	0.362	0.116	5/32" Allen	0.750	Flat Head
1/4"-20	0.458	0.153	3/16" Allen	0.750	Flat Head
5/16"-18	0.567	0.191	1/4" Allen	0.875	Flat Head
3/8"-16	0.675	0.230	5/16" Allen	1.000	Flat Head
1/2"-13	0.893	0.306	3/8" Allen	1.250	Flat Head
#4-40	0.225	0.066	3/32" Allen	0.500	Button Head
#6-32	0.279	0.082	7/64" Allen	0.500	Button Head
#8-32	0.332	0.098	9/64" Allen	0.625	Button Head
#10-24	0.385	0.114	5/32" Allen	0.750	Button Head
1/4"-20	0.437	0.132	3/16" Allen	0.750	Button Head
5/16"-18	0.547	0.166	3/16" Allen	0.875	Button Head
3/8"-16	0.656	0.199	1/4" Allen	1.000	Button Head
1/2"-13	0.875	0.265	5/16" Allen	1.250	Button Head

No fasteners match your search. Try a different term or filter.

Notes on This Chart

Socket head cap screw dimensions per ASME B18.3 (imperial) and ISO 4762 (metric).
Hex bolt dimensions per ASME B18.2.1. Head diameter shown is across-flats (AF).
Flat head (countersunk) dimensions are for 82-degree angle per ASME B18.3.
Thread lengths shown are standard for bolts up to 6 inches long.
Always verify dimensions against the specific manufacturer's data sheet.

Need precision fastener components?

Upload your CAD file for an instant quote. Free DFM review included with every order.

Upload CAD for Instant Quote

Frequently Asked Questions

What is the difference between a socket head cap screw and a hex bolt?

A socket head cap screw (SHCS) has a cylindrical head with an internal hex (Allen) drive, allowing it to sit flush or below the surface in a counterbore. A hex bolt has a six-sided external head driven with a wrench or socket. SHCS are common in machine assemblies where space is tight, while hex bolts are used in structural and general-purpose applications.

How do I measure bolt head diameter?

For socket head cap screws and button head screws, measure across the widest point of the cylindrical head. For hex bolts, measure across the flats (wrench size) or across the corners. The across-flats dimension is the standard wrench size used to tighten the bolt.

What is a flat head screw and when should I use one?

A flat head screw (also called a countersunk screw) has an 82-degree or 90-degree conical head designed to sit flush with the surface. Use flat head screws when you need a smooth surface with no protruding hardware, such as on cover plates, fixtures, and consumer products.

What wrench size do I need for a given bolt?

The wrench size depends on the bolt type. For socket head cap screws, you need an Allen key matching the internal hex drive size. For hex bolts, you need a wrench matching the across-flats dimension of the hex head. This chart lists both drive sizes and wrench sizes for quick reference.

Are metric and imperial bolt head proportions the same?

No. Metric socket head cap screws (ISO 4762) have slightly different head height-to-diameter ratios compared to imperial SHCS (ASME B18.3). Metric hex bolt heads (ISO 4014) also differ from imperial hex bolt heads (ASME B18.2.1). Always refer to the correct standard for your fastener system.

Explore

More Resources

Thread Chart | UNC Thread Dimensions Reference Tap & Drill Size Chart | UNC, UNF & Metric Thread Sizes Dowel Pin Size Chart | Standard & Oversized Dimensions Retaining Ring & Snap Ring Size Chart | Groove Dimensions Countersink Size Chart | Screw Size to Hole & Angle Reference Material Hardness Chart | Brinell, Rockwell & Vickers Comparison

Ready to Start?

Get Your Parts Made Right

Upload your CAD file and get instant pricing. Prototypes ship in as few as 3 days.

Get an Instant Quote Email Us

No minimums · 100% Made in USA · Never brokered · Ships anywhere in the US

Ready to machine your part?

Upload CAD for Instant Quote