Crank Arms

[jamesxyz]

Will Crank arms fit any bike or are they BB specific?

I ask as I saw some 105s (and Ultegras for that matter) going cheap on ebay and mine are cheapy Bontrager that came on the bike (Trek 1.5) but didn't want to bid in case they didn't fit.

Any advice will help as I'm not too tech savvy but want to learn!

 

[TheDoctor]

Well, crank arms need the correct BB, but BBs are not expensive.
The main ones you're likely to find are :-
Hollowtech 2 - these use external bearings, and the axle is an integral part of one crank
Hollowtech - these are a splined BB, that wasn't about for very long
Square Taper - the old-fashioned sort, been around since dinosaurs roamed the Earth.

These all screw into a standard frame.

Either way, a new BB will cost £10-20 or so. They're not expensive. I have to say, though, that I'd personally upgrade the wheels and tyres long before the chainset.