One inch equals exactly 25.4 mm, so no metric socket size converts to a perfectly “round” SAE fraction — every metric-to-inch match below is a nearest-fit approximation, not an exact one. The chart below gives the closest 1/32″ fraction for common metric sizes from 6 mm to 32 mm, alongside the actual metric and inch (SAE) size ranges we cut on our own 1/2″ drive socket line.
Why Metric and SAE Sizes Don't Line Up Exactly
Because 1 inch is fixed at 25.4 mm, converting any metric dimension to inches produces a decimal value, and standard SAE sockets are only cut in fixed fractional steps (typically 1/32″ increments). The nearest fraction to a given metric size is sometimes very close — 19 mm is only 0.05 mm from 3/4″ (19.05 mm) — and sometimes noticeably off, such as 17 mm sitting roughly 0.33 mm away from the nearest 21/32″ fraction. A substitute socket that is a good fit on one bolt size can be a poor, corner-rounding fit on the next size up or down.
Metric to SAE Quick-Reference Conversion Chart
| Metric (mm) | Decimal inch | Nearest SAE fraction | Fraction as mm | Difference |
|---|---|---|---|---|
| 6 | 0.2362″ | 1/4″ | 6.350 mm | +0.350 mm |
| 7 | 0.2756″ | 9/32″ | 7.144 mm | +0.144 mm |
| 8 | 0.3150″ | 5/16″ | 7.938 mm | −0.062 mm |
| 9 | 0.3543″ | 11/32″ | 8.731 mm | −0.269 mm |
| 10 | 0.3937″ | 13/32″ | 10.319 mm | +0.319 mm |
| 11 | 0.4331″ | 7/16″ | 11.112 mm | +0.112 mm |
| 12 | 0.4724″ | 15/32″ | 11.906 mm | −0.094 mm |
| 13 | 0.5118″ | 1/2″ | 12.700 mm | −0.300 mm |
| 14 | 0.5512″ | 9/16″ | 14.287 mm | +0.287 mm |
| 15 | 0.5906″ | 19/32″ | 15.081 mm | +0.081 mm |
| 16 | 0.6299″ | 5/8″ | 15.875 mm | −0.125 mm |
| 17 | 0.6693″ | 21/32″ | 16.669 mm | −0.331 mm |
| 18 | 0.7087″ | 23/32″ | 18.256 mm | +0.256 mm |
| 19 | 0.7480″ | 3/4″ | 19.050 mm | +0.050 mm |
| 20 | 0.7874″ | 25/32″ | 19.844 mm | −0.156 mm |
| 21 | 0.8268″ | 13/16″ | 20.637 mm | −0.363 mm |
| 22 | 0.8661″ | 7/8″ | 22.225 mm | +0.225 mm |
| 23 | 0.9055″ | 29/32″ | 23.019 mm | +0.019 mm |
| 24 | 0.9449″ | 15/16″ | 23.812 mm | −0.188 mm |
| 25 | 0.9843″ | 31/32″ | 24.606 mm | −0.394 mm |
| 26 | 1.0236″ | 1-1/32″ | 26.194 mm | +0.194 mm |
| 27 | 1.0630″ | 1-1/16″ | 26.987 mm | −0.013 mm |
| 28 | 1.1024″ | 1-3/32″ | 27.781 mm | −0.219 mm |
| 30 | 1.1811″ | 1-3/16″ | 30.162 mm | +0.162 mm |
| 32 | 1.2598″ | 1-1/4″ | 31.750 mm | −0.250 mm |
Figures are calculated directly from the fixed 1 inch = 25.4 mm conversion factor and rounded to the nearest 1/32″; they are a reference for identifying the closest commercial size, not a substitute for measuring the actual fastener.
Transtime's 1/2″ Drive Socket Range — Metric and Inch (SAE)
As a socket manufacturer we cut dedicated metric and inch tooling rather than relying on nearest-fit substitution. Our 1/2″ drive hand socket line runs the following size series, each machined to its own nominal dimension rather than converted from the other:
| System | Sizes manufactured |
|---|---|
| Metric (mm) | 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32 |
| Inch / SAE | 5/16″, 11/32″, 3/8″, 7/16″, 15/32″, 1/2″, 9/16″, 19/32″, 5/8″, 21/32″, 11/16″, 3/4″, 25/32″, 13/16″, 7/8″, 15/16″, 1″, 1-1/16″, 1-1/8″, 1-3/16″, 1-1/4″ |
When a Nearest-Fit Substitution Is (and Isn't) Acceptable
Slipping a close metric size onto an SAE bolt, or the reverse, can work at low torque and for a single use, but the mismatch shown in the chart above concentrates load on fewer contact points inside the hex, which rounds off fastener corners faster and can slip under higher torque — a risk that rises further on soft or corroded fasteners. On anything beyond a light, one-off job, using a socket cut to the fastener's actual standard is the safer choice.
Shop Metric and SAE Sockets
We manufacture 1/2″ drive hand sockets and 1/2″ drive bit sockets in both metric and inch series, plus complete socket sets across other drive sizes. For a specific size range or private-label set, contact our team.