Measuring Chain Ring Bolts

     There is some confusion over Chain Ring bolts on bicycles. Below I wrote some information that can also be found here:How To Measure Bolts

There are 2 main types of chain ring bolts.

For road and track applications you want to use "singles". This 

attaches a single chain ring to the crank spider. Closed spacing is 

about 4mm.

For Downhill and MTB you want doubles. This attaches 2 chain 

rings to the spider. Closed spacing is about 6.2 to 6.8mm.

Spacing: The spacing needs to be less than the chain ring stack to 

it will tighten properly.

Inner chain rings use a "Granny Bolt" and no nut is needed. This 

bolt is about 10mm long.

Hex Backed Bolts  These have a short bolt section and cannot be 

used with much over a 8mm gap. The bolt doesn't have as much 

threading.

Slotted back nuts allow a much longer bolt and can handle chain 

ring spacings between 6.2mm to 11mm.

The head of these bolts will engage with the outside chain ring to 

center if the nut is not long enough.

All are 8mm bolts - 0.75 pitch (Extra fine)

Nuts are made to be in a 10mm bore.