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how are chainring bolts measured?

dexterq20

Turbo Monkey
Mar 6, 2003
3,442
1
NorCal
Having some issues with chainring bolts that are a bit on the short side - they'll tighten down, but there's very little thread engagement, which caused the threads on one of the bolts to strip out last night when I attempted to install a new chainring.

I know the bolts are measured in lengths (generally ranging between 8 and 10mm or so) - but what is this measuring? The length of the bolt? The length of the nut? Or something else? The bolts I have measure 9.5mm (excluding the head), and the nuts are 8mm.

FWIW, I'm running Holzfeller crank arms with an e13 Turbocharger and Guide Ring - any specific suggestions for chainring bolts that will work with this setup?
 

dexterq20

Turbo Monkey
Mar 6, 2003
3,442
1
NorCal
Nice, thanks.

So when I'm "shopping" for new bolts, is the listed length referring to the length of the bolt (and not the nut)?
 

Arkayne

I come bearing GIFs
May 10, 2005
3,738
15
SoCal
Clarify with the seller. I've seen them listed as Total Length or the bottom of the head. For example, a 14mm total length or 12mm from bottom of head.
 

stoney

Part of the unwashed, middle-American horde
Jul 26, 2006
21,514
7,058
Colorado
Nice, thanks.

So when I'm "shopping" for new bolts, is the listed length referring to the length of the bolt (and not the nut)?
The easiest way to confirm what you need it to measure the width of your bashguard, chainring and the crank. Once you know those measurements, make sure the rear (female) end is less than the combined width of the crank and chainring. Then get a bolt (male end) that is long enough to have good overlap of the female end.
ie. chainring 4mm, crank 5mm, bashguard 5mm. You need 14mm combined length, with a female end no longer than 9mm. So get a 7 or 8mm female end with a 12mm male end. You will end up with 5mm of overlap that way.

and go to a bike shop for this. Bolts only cost $1 each at most shops.