As HillRider says, the plastic adapter ring sits inside the older Hollowtech II tools to allow them to fit the newer BB60 cups. They are smaller in diameter by around 3-5mm. It just saves buying a newer, smaller headed tool. I had to use this tool on two BB's I just fitted for myself and a friend.

Good call regards the NDS spacer, too. My bike is a compact double, my friend's is a triple. I overlooked this spacer at first, so off came the crank arm, on went the spacer and crank arm then nipped up to spec with a torque wrench.

I tend to turn the little crank arm cap finger tight, then a little more and then back off a tiny amount and then tighten ever so slighty again. Just feel the bite and then back off and tighten again. Worked so far for years.