I just used a 1/4" drill bit, seemed to work perfectly. I tried to slide the prop onto the shaft of the drill bit (opposite side of the blades) and it was a snug fit-it would slide on if you turned the prop, just like the fit that was on the engine shaft. I put the bladed side of the bit in the prop, and 'threaded' the prop onto the drill bit, and was able to slide the prop back off the drill with only a very slight turning of the bit. Now prop just slides over threads of shaft, and needs only a slight push to get the prop fully down to the end of the shaft. Should be a perfect fit