you need to know the prop shaft size and also the id of the packing nut...when you find thoses out you subtract the shaft size from the id of the packing nut and devide the diff by 2 that will tell you how thick the packing needs to be ...most take three layers of packing ....there is a thread going on now about this packing ...you may want to read it ...also ther is a artical by Main Sail on repacking in Compass Marine...it will be very helpful as well...
regards
woody