I haven't seen anybody mention these as a source of lead. I work at the local electric company and ran across some insulator pins in the scrap hopper. I soon made a deal to cast some sinkers for the linemen and stores keepers if they would throw these in a box for me. The lead alloy is in the threaded end. It doesn't seem to be pure lead, but possibly something close to wheel weights.
Anyhow, if this becomes a lead source for a couple of people who currently don't have one, it will be worth the thread.