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
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
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.