I use the Higley acorn shaped ones with hex sides and matching nuts on all my 4 strokes. They're light and easy to tighten with a crescent wrench:
http://www3.towerhobbies.com/cgi-bin...&I=LXL745&P=ML
These are the lock nuts I was talking about for 4 strokes but you probably won't need it for your ST:
http://www3.towerhobbies.com/cgi-bin...?&I=LXL743&P=M