I was sure my father was pulling my leg. 
I was about 7 years old and he said that he had a two headed nail. 
I couldn’t think of a use for such a thing and told him he must be kidding. 
Until that day I had never seen a scaffolding nail. 
I don't see them anymore. Most people used steel scaffolds, scissor lifts, or
bucket lifts.
When I went looking for that nail tonight I couldn’t find it in the tool box.
Must have strayed during the last move. It may still turn up. I’m saving it for
tricking my grandchildren.