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
Bolt size vs Wrench size??
Apr 11, 2004
2 Replies
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
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 8mmUnited 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
Join the Discussion
Have something to add? Share your thoughts — no account required.
Didn't find your answer?
Ask the community — no account required