Temporarily fitting a small chainring to an old Stronglight single crank with a swaged arm. The single chainring is also effectively the spider (it's just machined from a flat piece of alloy), and has a currently unused 86BCD set of holes in it.

So I have big ring - 3.5mm spacer - small ring.

The chainring bolts I have to hand are 7mm long, which is just over 2mm short of the actual measured stack depth. The bolt is getting less than half way through the chainring. At present I can get about three threads engaged, which is probably suboptimal. I think a 9mm long bolt would be perfect.

Not sure if this all works by the clamping force of chainring against 'spider' (in which case I'm probably OK) or whether the chainring bolt body actually bears load in the direction of rotation (seems that getting the bolt almost all of the way through would be more important then).