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Wrench & Socket Size Chart
Quick answer: 3/4″ = 19 mm (2 thou apart, interchangeable) and 5/16″ = 8 mm (2.5 thou). 1/2″ and 13 mm are 11.8 thou apart — usable but snug. There is no SAE equivalent for 10 mm.
Every SAE and metric wrench size side by side with the exact gap in thousandths of an inch, so you can tell a safe substitution from one that will round the head off.
SAE to metric wrench conversion chart
The gap column is what matters. Anything under about 6 thousandths of an inch is close enough that the wrong wrench will seat without rounding the fastener. Past twelve thousandths you will round it.
| SAE | Decimal (in) | Metric | Decimal (in) | Gap (thou) | Verdict |
|---|---|---|---|---|---|
| 5/32 | 0.1563 | 4 mm | 0.1575 | 1.2 | Interchangeable |
| 3/16 | 0.1875 | 5 mm | 0.1969 | 9.4 | Snug — care |
| 7/32 | 0.2188 | 5.5 mm | 0.2165 | 2.3 | Interchangeable |
| 1/4 | 0.2500 | 6 mm | 0.2362 | 13.8 | Do not substitute |
| 9/32 | 0.2813 | 7 mm | 0.2756 | 5.7 | Interchangeable |
| 5/16 | 0.3125 | 8 mm | 0.3150 | 2.5 | Interchangeable |
| 11/32 | 0.3438 | 9 mm | 0.3543 | 10.5 | Snug — care |
| 3/8 | 0.3750 | 10 mm | 0.3937 | 18.7 | Do not substitute |
| 7/16 | 0.4375 | 11 mm | 0.4331 | 4.4 | Interchangeable |
| 1/2 | 0.5000 | 13 mm | 0.5118 | 11.8 | Snug — care |
| 9/16 | 0.5625 | 14 mm | 0.5512 | 11.3 | Snug — care |
| 5/8 | 0.6250 | 16 mm | 0.6299 | 4.9 | Interchangeable |
| 11/16 | 0.6875 | 17 mm | 0.6693 | 18.2 | Do not substitute |
| 3/4 | 0.7500 | 19 mm | 0.7480 | 2.0 | Interchangeable |
| 13/16 | 0.8125 | 21 mm | 0.8268 | 14.3 | Do not substitute |
| 7/8 | 0.8750 | 22 mm | 0.8661 | 8.9 | Snug — care |
| 15/16 | 0.9375 | 24 mm | 0.9449 | 7.4 | Snug — care |
| 1 | 1.0000 | 25 mm | 0.9843 | 15.7 | Do not substitute |
Gap is the absolute difference in thousandths of an inch between the SAE and metric opening. Verdicts assume a six-point socket on a fastener in good condition; a twelve-point on a rounded head needs a tighter match.
Six-point vs twelve-point
A six-point socket bears on the flats of the fastener. A twelve-point bears closer to the corners, which is where the metal is thinnest. On anything tight, rusted or already slightly rounded, six-point is the only sensible choice — the extra engagement angles of a twelve-point buy convenience at the cost of grip.
| Six-point | Twelve-point | |
|---|---|---|
| Contact | On the flats | Near the corners |
| Engagement positions | Every 60° | Every 30° |
| Best for | High torque, rusted, rounded | Tight quarters, low torque |
| Rounding risk | Low | Higher |
Drive sizes and their torque ranges
| Drive | Typical socket range | Practical torque | Where it belongs |
|---|---|---|---|
| 1/4″ | 4–14 mm, 5/32–9/16″ | Up to ~25 lb-ft | Trim, electronics, small engine work |
| 3/8″ | 8–19 mm, 5/16–3/4″ | ~10–100 lb-ft | The general-purpose drive |
| 1/2″ | 10–32 mm, 3/8–1-1/4″ | ~30–250 lb-ft | Suspension, lug nuts, structural bolts |
| 3/4″ | 19–50 mm | 200–600 lb-ft | Heavy equipment |
Using a breaker bar on a 3/8″ drive to free a lug nut is how drives snap. Match the drive to the torque, not to the socket you happen to own.
Frequently asked questions
What metric size is closest to 1/2 inch?
13 mm. A 1/2 in wrench is 0.5000 in and 13 mm is 0.5118 in, a gap of 11.8 thousandths. It will seat but it is loose — fine on a clean steel fastener, risky on aluminium or anything already rounded.
Is 3/4 inch the same as 19mm?
Effectively yes. 3/4 in is 0.7500 in and 19 mm is 0.7480 in — two thousandths apart, which is inside normal manufacturing tolerance. These two are genuinely interchangeable.
What is 10mm in SAE?
There is no exact match. 10 mm is 0.3937 in, sitting between 3/8 in (0.3750) and 7/16 in (0.4375). A 3/8 in wrench is 18.7 thousandths too small and will not go on; a 7/16 in is 43.8 thousandths too large and will round the fastener. Use the 10 mm.
Why do I keep losing 10mm sockets?
Because 10 mm is the most common fastener size in automotive and appliance work, so it spends more time out of the set than any other socket. There is no mystery beyond usage frequency — but it is a real and widely shared experience.