The prop reamer is a must. It is the only way to keep the hole centered correctly. Now comes the rub, you need two, a fraction and a metric.

Most props start life with a 1/4" bore. THis fits most smaller engines, but some engines have a metric size prop shaft, IE a saito. The Magnum 52 and the O.S 52 four strokes have a 1/4" shaft, THe Magnum 70 and 91 four strokes have a 5/16" shaft. My saito four stroke has a shaft in MM, don't remember the size.

Towere sells both a metric and fractional reamers, both with a 1/4" pilot on them. They are money well spent.

The prop should fit with a frictioin fit to the shaft. IE slide over the thread, but get a slight resistance when it goes on the shoulder on the prop shaft near the hub. Usually a well fit prop will spin on up to the hub, but be a little slugish to push on. A loose fit prop is a problem waiting to happen, No mater how well you balance the prop, it is all but impossible to get it centered, so it will run out of balance. This is hard on the plane and on the engine.

I picked up a batch of 12x6 Zinter wood props on Ebay when I first started flying, It turns out that they were all bored to 0.260", a sloppy fit on the engine. I made a thin bushing from 0.005" brass shim stock and they were fine after going that route. I also used the same size prop on the 52 and 70 four strokes, so I reamed them out to a 3/8 and then made a set of bushings for 1/4" 5MM and 5/16" shafts and I could swap probs at will.

Don