RE: OS 46 powered TC31 the making...
I use 3/16 in shafts for .45 and below and 1/4 inch shafts for .67 and above. Haven't had a problem with shaft breakage. As HR said, grease the shaft before each day of racing. I actually grease them at the end of the day during a multi-day event. Takes less than 5 minutes per boat. It also gives you a chance to do a quick visual to spot any unusual wear.