Prop Shaft Packing
I've used the GFO packing also with great results. I installed all new packing 3 1/2 years and about 600 hours ago and only had to adjust one side recently. Great stuff.
The only way to determine what size you need is to measure it. Open up your packing gland and measure the inside diameter, subtract the shaft diameter and cut that figure in half. I have 1 3/4 shafts and seem to remember I used 3/8, or was it 1/2"? Don't remember for sure.