8 mm to SAE — Closest Inch / Fraction Equivalent

8 mm converts to approximately 5/16" (0.3125" or 7.94 mm exact). exact match — safe substitute either direction.

Quick answer: what is 8 mm in SAE?

The closest SAE wrench / socket size to 8 mm is 5/16", which equals 7.94 mm. The difference is 0.06 mm — effectively interchangeable on any bolt.

Is 5/16" the same as 8 mm?

Not quite — 5/16" = 7.94 mm, so the SAE size is slightly smaller than 8 mm by 0.06 mm. exact match — safe substitute either direction.

When can I substitute 5/16" for 8 mm?

Use the SAE substitute when (1) the bolt head is clean and sharp — no rust, no prior rounding, (2) you have a 6-point socket not 12-point, and (3) torque is moderate. For breaking loose a seized bolt, anything safety-critical (suspension, brakes, head bolts), or impact-driver use, always use the correct metric size. Honda, Toyota, and most Japanese OEMs spec metric and have tight head clearances — do not substitute on those vehicles.

Does the same logic work for 5/16" to mm?

Yes. 5/16" to mm = 7.94 mm. A 8 mm socket on a 5/16" bolt will be slightly loose (overshoot by 0.06 mm).

Full mm to SAE wrench & socket conversion chart

Quick reference for every common size — 8 mm = 5/16", 9 mm = 11/32", 10 mm = 3/8", 11 mm = 7/16", 12 mm = 15/32", 13 mm = 1/2", 14 mm = 9/16", 15 mm = 19/32", 16 mm = 5/8", 17 mm = 11/16", 18 mm = 23/32", 19 mm = 3/4", 21 mm = 13/16", 22 mm = 7/8", 24 mm = 15/16", 27 mm = 1-1/16", 30 mm = 1-3/16", 32 mm = 1-1/4", 36 mm = 1-7/16", 41 mm = 1-5/8". These are closest-fit tool sizes, not exact math; see the notes above for the exact millimetre difference and whether each swap is safe on a real bolt.

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