SHOP REFERENCE / METRIC SOCKETS
Metric Socket Size Chart
Choose a socket by the width across the flat sides of the nut or bolt head. The chart lists common metric openings from smallest to largest; check the size stamped on your socket and test the fit on the actual fastener.
Open the Socket Finder toolA 10 mm socket has a 10 mm opening. M10 describes a bolt’s nominal thread diameter; its hex head can be another size.
Common metric socket sizes
Examples apply to standard external hex heads only; a different fastener style or standard may use a different head size.
| Socket opening | Example or fitting note |
|---|---|
| 4 mm | Small hex fasteners |
| 4.5 mm | Small hex fasteners |
| 5 mm | Small hex fasteners |
| 5.5 mm | Small hex fasteners |
| 6 mm | Small hex fasteners |
| 7 mm | Standard M4 hex bolt head |
| 8 mm | Standard M5 hex bolt head |
| 9 mm | Hex heads measuring 9 mm across flats |
| 10 mm | Standard M6 hex bolt head |
| 11 mm | Hex heads measuring 11 mm across flats |
| 12 mm | Hex heads measuring 12 mm across flats |
| 13 mm | Standard M8 hex bolt head |
| 14 mm | Hex heads measuring 14 mm across flats |
| 15 mm | Hex heads measuring 15 mm across flats |
| 16 mm | Modern ISO M10 hex bolt head |
| 17 mm | Older DIN M10 hex bolt head |
| 18 mm | Modern ISO M12 hex bolt head |
| 19 mm | Older DIN M12 hex bolt head |
| 20 mm | Hex heads measuring 20 mm across flats |
| 21 mm | Modern ISO M14 hex bolt head |
| 22 mm | Older DIN M14 hex bolt head |
| 23 mm | Hex heads measuring 23 mm across flats |
| 24 mm | Standard M16 hex bolt head |
| 25 mm | Hex heads measuring 25 mm across flats |
| 26 mm | Hex heads measuring 26 mm across flats |
| 27 mm | Standard M18 hex bolt head |
| 28 mm | Hex heads measuring 28 mm across flats |
| 29 mm | Hex heads measuring 29 mm across flats |
| 30 mm | Standard M20 hex bolt head |
| 31 mm | Hex heads measuring 31 mm across flats |
| 32 mm | Older DIN M22 hex bolt head |
This chart shows a practical range, not the contents of any one kit. Some sets omit intermediate sizes or include larger ones. An example bolt head size is a nominal reference for that standard, not a substitute for measuring your fastener.
CHOOSE THE SOCKET
6-point vs 12-point
Fits external hex heads at six positions. A snug 6-point socket is a useful first choice for high torque or a worn hex head because it has a broader fit against the hex flats.
Fits an external hex head in more starting positions and also fits a matching 12-point fastener. It can be convenient where ratchet movement is limited. Use the exact opening size and a snug fit.
Neither point count changes the opening size: a 13 mm socket is marked 13 mm in either style. The 1/4, 3/8, or 1/2 in. drive size is the square opening for the ratchet, not the size that fits over the fastener. Use an impact-rated socket with an impact wrench.
Match a bolt thread size to its hex head → See metric and SAE sizes in order →Sources and scope
TEKTON’s 4–15 mm set, 6–24 mm set, and 10–32 mm set document the listed socket sizes. Bolt Depot’s metric bolt head dimensions support the standard hex head examples. GEARWRENCH’s 12-point socket details describe hex and 12-point fit. Head style and manufacturing standards matter; measure across flats and confirm the fit.