On 9/25/2014 7:49 AM, William Engle Sr wrote:
> 15 and 18 mm are used more in the US than the rest of the world.
There's different standards on what size bolt head you get with a given
size threaded shank.
F'rinstance, a Japanese M8 bolt will be a 12mm head, but a Euro (or
usually US) DIN M8 bolt will be a 13mm head and you'll pretty much never
find anything that takes a 12mm socket on a German car.
For some years Detroit, in particular, chose their metric fastener head
sizes to be close enough to let you use SAE wrenches - and while we all
know to grab an 8mm for a 5/16 head and vice-versa, 1/2in fits most
13mm, 5/8 usually fits 16mm, 19mm and 3/4 are interchangeable as are 7/8
and 22mm, the true Detroit oddity of the '80s was the M6 fastener with
the 11mm head sized to fit a 7/16 wrench.
Many older M12 fasteners and lots of parts-store M12s are 19mm head but
I think most every mfr now (as true of my BMWs as my Suburban) uses 18mm
heads on their M12s.
If you're wrenching on any German product in the last dozen years you're
going to need a set of 'outie' Torx sockets, though...
John.
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