Most of my props will be a little tight when I first get them. I'll screw them onto the engine shaft then use the nut to tighten them up the rest of the way. It only takes a couple times and the props go on and off with no problems.

I do think that the 10x6 prop is a bit on the small side for the 46FX. I use 11x6 APC sport props on my 46FX and it pulls pretty nice. The engine may rev a little high with a 10x6 prop. Although, if it's on your first trainer, it'll work for now. Try a 10x7 or the 11x6 on it though. I think you'll like it better.