Thickie question here!
I need a new crank arm bolt for my Sora 3500 crank and I've bought the wrong one - the one I bought is for Sora 3400 and the thread diameter is too small (I wondered why it just span round and round when I tried to tighten it up!).
I've searched the web and can't find anything specific for sora so i'm presuming that all the more recent cranksets use the same size bolt? I've also seen lots of bling aluminium ones on ebay (compared to shimano plastic) with a 20mm thread diameter, would these fit. They also appear to be hollow, rather than blanked. I'm presuming the genuine shimano one is blanked for a reason?
Shimano use a plastic one so you don't tighten it too much as it's just to get the right pre-load into the bearings. It doesnt actually hold the arm on, the clamps on the non-drive side do that.
they do seem to list a few different ones but I'm not sure (except for some of the XTR ones) if there is a difference to any.
If you look on the shimano tech docs website it will give you a part number and normally cross reference to the same part from other models.