Hex wrench size accuracy

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2012-08-01 12:01 PM

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Subject: Hex wrench size accuracy
I have a set of Pedro's and Spin Doctor hex wrenches and have noticed quite often that the fit on bolt heads aren't tight thereby leading to stripped heads over time. Which item would tend to be miss-sized, the wrench or the bolt head? Happens on different bikes so I know something's not right. Anyone have this issue with these brands or others?

2012-08-01 12:29 PM
in reply to: #4341335

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Elite
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Subject: RE: Hex wrench size accuracy

bingo.

Fasteners are also to blame, especially plated, painted and anodized fasteners. The finishing process change the size of the turning recepticle on the bolt.

Better quality tools, Park, Wiha, Snap-On, Pedros, etc. have good tolerances and seem consistent. Others, not so much.

2012-08-01 12:34 PM
in reply to: #4341424

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Subject: RE: Hex wrench size accuracy
Guess I'll have to go shopping, rats! And keep some spare bolts at hand. Thx
2012-08-01 3:17 PM
in reply to: #4341335

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Regular
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Subject: RE: Hex wrench size accuracy

The specs for normal grade fasteners have a lot of leeway, Add that to a tool that was finished at one end or the other of allowable specs and you can end up way too tight or way too loose. Just a fact of adding allowable tolerances together.

Try welding steel pipe together end to end when you get out to the edge of out of round limitations.

2012-08-01 3:40 PM
in reply to: #4341335

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Master
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Rural Ontario
Subject: RE: Hex wrench size accuracy

another possibility: Metric vs. Imperial...  some sizes seem almost identical i.e. 5/16" may seem the same as 8mm....

2012-08-01 3:59 PM
in reply to: #4341977

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Subject: RE: Hex wrench size accuracy
Good point Mark. I'm usually careful about that. Some bolts I know are metric, such as my wheels, but others I'd need to confirm with the mfg. Seems though that most bikes are metric and the tools sold in bike shops are also metric. I use Park Tools Blue Book for guidance and I think just about every spec is for metric. Never hurts to double check.

2012-08-01 4:12 PM
in reply to: #4341335

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Pro
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Subject: RE: Hex wrench size accuracy
Tom got it right... you have to stack the tolerances between the hex key and the hex bolt head. If a bolt is at the min. tolerance and the key is at max, you may have a hard time getting the key properly seated and slip. Same thing goes for a key at min and bolt head at max, then you may have too loose of a fit and slip.

They keys will be easier for you to control as a customer, so spend money on a good, high quality set (they're not that expensive...).
2012-08-01 4:21 PM
in reply to: #4342063

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Subject: RE: Hex wrench size accuracy

I know what you're describing. My Easton wheels have a preload adjustable hub requiring a 19mm wrench but the wrench hardly fits 'cause of all the coatings. My wrench for that app btw is a Park Tool.

It only gets expensive when having to purchase replacement tools!

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