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 of the end of the pirn.
The 6" pirn fits the Schacht 12" end-delivery shuttle. Its overall length is 6 1/4".
The 8" pirn fits the Schacht 15" and Bluster Bay 15" end-delivery shuttles. Its overall length is 7 7/8".
Pirns wind best on a double-ended winder.