When ordering a fixed pitch aircraft propeller, it is important to know the difference between a tapered crank shaft and a flanged crank shaft.  Be sure to alert your sales person as to which you have.  The bolt kit for each is different and not interchangeable.  A tapered shaft may require bushings in the back of the propeller.  A tapered crank shaft is pictured top right and a flanged crank shaft is pictured bottom right. 

Tapered Crank Shaft or Flanged Crank Shaft?