SG is a pilot shaft, it's longer then a short crank, but the end of it is not threaded, that image a few posts above mine is an SG. A short shaft would be cut off about where the theading stops. If you bought a TC3 kit you have the nut for either type. Your instruction book shows you how to install on either type. Basicly the different in nuts is that the short shaft nut screws on to hold the flywheel on tight, and the other end of this nut extends for you to put the clutch housing onto. With the polit shaft nut it doesn't have the extention, so you slide the clutch bell over the accuall shaft. I don't know if the RTR comes with both nuts, I doubt it.. If you have the RTR take it out, take the clutch apart and see which type you have.

If you need I can scan the pages of my instruction book that show you how to assemble this part of the car. Just PM me.