Ok, he doesn't mention using bull pins (unles I missed it elsewhere), but mentions using tool steel, structural or mild steel. The example of a hammer eye drift he illustrates in the book is for a monkey tool. He says he has hammer eye drifts made from 5/8" round up to 1 1/8" round in 1/8" increments and a single tool that is 16" or so long of 1 1/8" tapering down to 3/8" round and then made oval (hammer eye) in section that he uses to put the hourglass shape in his hammers. I can try to look up other things if you need me to. Since I don't know first hand, I'm just giving you what I'm reading.