Cranks for a Haro Zippo, how do i know they fit

[monkeybat]

Looking to buy new cranks how do you know what size fits, how are they measured ? Twenty odd years ago there seem to be only one size.

[harris]

the bottom bracket will be an american one the bigger ones with cups.
some are loose ball ala one piece like old school
or sealed 3 piece   
the arm length is down to you most use 175 as an average.
old school cranks will fit yours  and upto around 2005 some changed to smaller bbs
profile or twin pinch flight cranks will work spot on
the bb on average will be 19mm or some 20mm get that bit right and you can use mixed bottom brackets with cranks.
so basically your bb needs to be an american one   aim for a 19mm hole  then crank choice is yours for 3 piece at 19mm
or cheaper 1 piece is easy most will fit

[Spen69]

^^^ what he said^^^ 

It's a standard American size so you can get a one-piece into it if you want I had one and gave it to my brother as I didn't know what it was
 
Spen

[harris]

also take ito account you pedals  9/16 for 3 piece   1/2 for 1 piece  apart from a few odd balls.

[monkeybat]

Cheers guys.