I'm sure you have solved the problem by now, but for others that may look to this thread for an answer....here it is.

I had the same problem. GWS just makes all their props with 3mm holes. You will just need to drill the hole a little larger for your use.

The Slow Stick 400 will require a 5/32" drill to make the hole the proper size. The drill will self center when you start the drill down since there is already a hole. Drill a couple while you are at it.

Have fun!

Cliff