Im a newbie and i was on danscomp about to buy an Odyssey thunderbolt cranks when it said that i need to buy a bottom bracket to have a complete crankset.what is a bottom bracket and do i have to buy one ?.doesn't the cranks come with everything needed to install it to the bike?Why do they all look different and do i have to buy a specific one for the Odyssey cranks?i have a stock subrosa bike,will the bottom bracket on my bike fit the cranks?