I currently use Porper ferules, bore them out to 3/8 of an inch for a 3/8 inch tenon. I use a .6 inch length ferule uncapped and usually cut the tip down by 50%-67%. Most of my shafts hit pretty straight with this setup and they are quite lively for imparting english. I would say the ferulles hold up fairly well because most players use a seperate break cue nowadays. I'm sure the ferulle would be under more stress with somebody pounding the break with it.