On an end-delivery shuttle, the pirn does not rotate around a pin like in a traditional boat shuttle. It fits snugly on the shuttle shaft and the yarn pulls off the end of the pirn.
The Bluster Bay pirn is 5 1/2" long and fits 13" Bluster Bay and short AVL end-feed shuttles. The 8" pirn fits Bluster Bay's 15" end-feed shuttles. For the 11" mini end-feed shuttle, you need the paper pirns.
Pirns wind best on a double-ended winder.