Dave, I have this problem on a BA 2320 that is front mounted and uses a collet type prop drive. I would tighten the prop nut to what seemed to be really tight, but it would slip on the motor shaft. I tried several different brands of collet mount and all were the same. I tried to open the slits in the collet and still would slip. Roughening with a dermal cutting wheel can help. What finally solved it for me was to keep the motor can from rotating while I got it tighten down the prop nut. On my motor/ship (profile) I used a thin rod (like 1/16" dia) that would slip through the back of the motor can air outlets (be careful that it does not touch the windings). This allowed that last half turn and got the collet tight to the shaft. If you have room a strap wrench around the could also work. I just saw a short video about using a piece of strap wrapped around a muffler and taking a pair of channel lock pliers to pinch it lose to the part and roll it back like a commercial strap wrench to loosen it. Could do the opposite to tighten if space is tight to get the commercial wrench in.

Best,    DennisT

Nylock

Left-handed props need left-handed prop nuts.  This is an option that the motor-makers should offer.  It's also an opportunity for machinists looking for a product.

While you're waiting, tighten it good and use Nylock.

The more you tighten the collet, the more you expand the collet. With the proper fitting collet and shaft, you only need to tighten the collet till snug. Collets are used daily to hold work or a cutter on a lathe or mill with significantly larger forces. Surface area is everything!

Kim