Dash,

On the one Asiatam gearbox I installed the output shaft was larger than the stock unit, so I first tried using a drill bit and a bit holder to manually enlarge the hole in the Stug III plastic sprockets. The problem I had was was the hole in the sprocket is flat bottom and the bevelled point on the drill bit started removing material and poked thru the sprocket. The other problem was the drill started to "auger" its way in and I couldn't open up the hole without drilling thru. I ended up ordering a reamer from McMaster Carr of the correct diameter for the Asiatam ouput shaft. The reamer has a flat bottom so it won't poke thru the sprocket, and the cutting surface is designed to specifically enlarge a hole rather than drill thru a hole. When I get home from work today I can post a link of the reamer I bought. The only thing you should do is verify the diameter of your output shaft before ordering the reamer. A micrometer with a diall indicator on it that you can buy for $20-30 from an auto supply store comes in extremely handy to measure part /shaft dimensions with a few thousands of an inch accuracy.

BTW, don't use power tools for this or you'll punch right thru the part. You need to by a bit holder that has a collet on it like drill that you turn by hand for the reaming process. I have used this approach on plastic and metal sprockets.

Frank