American Wrench Size Chart

Quick answer: American wrench sizes are usually SAE fractional inch sizes. The wrench fits the head or nut across the flats, not the threaded bolt diameter. For example, a 1/2 in standard hex bolt commonly takes a 3/4 in wrench, while a 1/2 in heavy-hex bolt takes a 7/8 in wrench.

SAE Bolt And Wrench Size Chart

Bolt diameter	Standard hex wrench	Heavy hex wrench	Note
#6	1/4 in	–	Small machine screw
#8	1/4 in	–	Small machine screw
#10	5/16 in	–	Small machine screw
1/4 in	7/16 in or 3/8 in	–	Head style can vary
5/16 in	1/2 in	–	Common light hardware
3/8 in	9/16 in	–	Common shop hardware
7/16 in	5/8 in	–	Common shop hardware
1/2 in	3/4 in	7/8 in	Heavy hex is larger
5/8 in	15/16 in	1-1/16 in	Large hardware
3/4 in	1-1/8 in	1-1/4 in	Large hardware
7/8 in	1-5/16 in	1-7/16 in	Heavy hardware
1 in	1-1/2 in	1-5/8 in	Heavy hardware
1-1/4 in	1-7/8 in	2 in	Industrial hardware

SAE To Metric Close Reference

SAE wrench	Decimal inches	Approx. mm	Fit warning
3/8 in	0.375	9.53 mm	Close to 10 mm, not identical
7/16 in	0.438	11.11 mm	Close to 11 mm
1/2 in	0.500	12.70 mm	Close to 13 mm, not identical
9/16 in	0.563	14.29 mm	Close to 14 mm
5/8 in	0.625	15.88 mm	Close to 16 mm
3/4 in	0.750	19.05 mm	Close to 19 mm
13/16 in	0.813	20.64 mm	Close to 21 mm
7/8 in	0.875	22.23 mm	Close to 22 mm

See also PVC Pipe Sizes Chart: Schedule 40, Schedule 80, and Thinwall Dimensions

Wrench Fit Tips

Measure across the flats when the correct size is uncertain.
Use a 6-point socket on stuck or rusty fasteners.
Do not force a loose metric substitute onto SAE hardware under high torque.

Check the bolt spanner size chart for metric comparisons.

Source Notes

SAE wrench sizes were checked against Bolt Depot’s US bolt head and wrench size chart, standard fastener references, and wrench conversion guides. Always match the actual head or nut, especially on old, damaged, or nonstandard hardware.