what crank do you have mate?
with cranks such as Sugino CT it does as the spindle is threaded....but with modern 3 piece with sealed bearings you just put one bearing into the frame/cup, then put the spindle through with the spacer on it, then put the other bearing in so you end up with the spacer inside the BB. Then it's simply a case of using the spacers to get the right distance between frame and crank arms/sproket. the sproket goes on and tightens onto the drive arm of the crank.
hope this helps?
it may not and others might do a crank dofferently
if it's a modern crank then go onto youtube and type in how to bmx and there's a great bit about doing the headset and cranks on new bikes
