Hi.
I was browsing Unicycle.Uk.Com, as I do, and I came across these
I dont know what they are, but could someone tell me where they go and what they do. It mentions that if are changing cottered cranks then you should be putting in new cotter pins.
Just curious!
Joe,
You don’t want to use cotterpins unless you have to. They are a horrible invention. A while ago a lot of bikes and unicycles came with cotterpins holding their cranks onto the axle. You wedge the soft metal cotterpins through holes in the cranks into grooves cut near each end of the axle on opposite sides (you can bash them with a hammer to get it snug). Once the cotterpins are in place you tighten the nuts on their ends to hold them (supposedly) securely.
The idea is that the harder metal of the axle should not be damaged by the softer cotterpins, so if there is wear and tear the pins can be replaced and the axle should stay intact. What happens is, as you ride, the cotterpins work themselves loose, and any riding done while they are loose destroys the pins, and eventually your axle (unless it’s hardened, in which case it’s not likely to have cotterpins). The cotterpins themselves do not cost much to replace, but it is annoying, and your cranks tend to end up out of sync. Avoid getting a Unicycle with cottered cranks if at all possible (my first one had them, I didn’t know better). Cotterless cranks/axles are far better, as replacement cranks are more readily available, and more user friendly. The best axle/crank combinations use splines which are far superior to cottered and cotterless cranks, but they are also more expensive and do not have as wide a range of crank lengths.
Thanks very much for that Rowan, you must have spent a few bit of time writing that!
Much Appreciated! 
Joe,