i have an OS 37, i got for free extra and i don't plan on buying another 30 size helicopter maybe a 50 but what else can i put it in like maybe a plane or something and if i will it fit 40 size planes?

It will but the problem you run into is the short crankshafts. By the time you put a thrust washer, prop and washer on it there's very little in the way of threads sticking out.

ok so i dont know anything about planes does that mean it wont fit a spinner on it and i dont know if you answered this i couldnt tell but will it fit in a 40 - 50 size plane ?

If you want a airplane engine, sell the .37 on RCU or Ebay and get a OS .46 for $110. It's cheaper and makes more power. This is the drive washer you need and by the time you put this on the shaft and a nut and washer you might be hard pressed to find a prop thin enough to fit.
http://www3.towerhobbies.com/cgi-bin...?&I=LXCL37&P=Z
As for it mounting, yes you can put it in a .40 size plane.