Bolt size vs Wrench size??

Been a while. but I know the wrench size is always 3/16" larger than the bolt but how does sizing go for metric fasteners? +1,+2 or +3.
Thanks

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On Sun, 11 Apr 2004 12:20:59 -0400, "Mastermech"

there isn't a set amount for metrics just as there is no set amount for SAE fasteners take a 1/2" bolt for example... the common head size is 3/4", however, an ASTM A325 (heavy hex grade 5) 1/2" bolt has a 7/8" head. there are also tight clearance 1/2" bolts that have a 12pt 5/8" head.
I've got 10 MM 9.8 fasteners with heads from 14-17 mm in size... depending on where I got them from. -Bret
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Actually there is no standard for the head flats in relation to the thread diameter. Here is a small section from the "Machinery Hand Book".
Metric Threads 8mm bolt = 13mm flats - difference 5mm 10mm bolt = 17mm flats - difference 7mm 12mm bolt = 19mm flats - difference 7mm 14mm bolt = 22mm flats - difference 8mm 16mm bolt = 24mm flats - difference 8mm
United National Threads 1/4" bolt = 3/8" flats - difference 1/8" 5/16" bolt = 1/2" flats - difference 3/16" 3/8" bolt = 9/16" flats - difference 3/16" 7/16" bolt = 5/8" flats - difference 3/16" 9/16" bolt = 7/8" flats - difference 5/16"
nospam
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