Joseph...
Adding to what Joel has replied.....the PT-25 doesn't need 'shims'. However, to clarify what is meant: In some cases if the rotor doesn't spin up with taxiing into the wind, putting 1/64" shims at the trailing edges of the rotor hub tangs will usually help. Start with 1/64 then if need be go to 1/32. However, the PT-25 comes with the SG6042 airfoil blades and as Joel says, these don't usually need any shims. The shims simply give each blade a bit of negative angle of attack, which helps getting the rotor to spin. However, too much negative angle of attack will cause the rotor to have less lift. This all has to do with getting the rotor into "autorotation".

Hope this helps.

Bill