I'm not very good at trimming nylon spinners.

I got rid of the nylon spinner on my trainer and replaced it with a "spinner nut." The spinner nut is aluminum (brass versions of some are also available) and replaces the steel nut that currently holds your prop on.

Here are links to different styles that will fit your 40FX.
http://www2.towerhobbies.com/cgi-bin...?&I=LXE158&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXHBR7&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXK241&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXL745&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXCC39&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXCC40&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXKE20&P=0

For many planes I think a spinner nut looks just as good as a spinner. For planes that need a real spinner, I either get my brother to do the trimming or get a Tru-Turn aluminum spinner. So far, my Tru-Turns have fit my props with no need of modification. I like them, but they are expensive. If you order direct from Tru-Turn you can have them cut the slots for the specific prop you're running.