RE: K&B 3.5
yes they are meant to slip on and off to replace the trust washer which goes between output shaft housing and the dog drive , the dog drive should have 2 allen set screws to tighten against the output shaft , i recommend a little loctite on each for vibration purposes. the thing you want to watch for is wear in the housing keep it well lubed with water proof grease and a well balanced prop or you are going to go through alot of output shafts , i found out the hard way , i have a k&b 7.5 outboard motor on a prather lap cat 2. well best of luck hope that was helpfull