Is there a rule of thumb to properly chose the correct size spinner size. Ihave 3 blade 13.5x8 prop.

thanks

The easiest fit all,safest,and to be honest best solution is [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXK242&P=0]CLICK[/link].. If you choose plastic or aluminum regular style spinners be sure the openings for the prop blades are larger then the blade. You do not want the propeller to have awkward pressure on it while it is spinning at 12,000 rpm.

Also make sure the spinner is not so big it blocks the cooling fins on the engine.

A general rule of thumb seems to be that a spinner is usually about 1/5 the prop diameter.