For the second time this year, I found several of these small cotter pins in a bicycle clean out, this one was an old shop that had closed down years ago, the guy ran it out of his basement. Much like another shop I cleaned out about four months ago these were in a small drawer along with a bunch of tapered pins. The pins go from about 5mm down to about 3mm. The cotter pins are short, about 1/3 the size of a normal crank cotter pin. They are 8mm in diameter and the threads are 5mm. The barrel part is about 14mm long. The cotter and nuts are steel, each one is used and slightly bent from removal.
The first time I found these I figured maybe it was some oddball older bike that used something like this for a seat post or something but someone else said maybe they're off a kids bike or tricycle of some sort?
The long pins are very hard steel, I can't scratch them with a hacksaw blade. Each one though appears turned on a lathe and parted with a cutting tool.
My first thought was that these were pins often used to repair casting cracks by a machinist but now that I again found these among bicycle parts, I figured I'd ask here. They are too hard and brittle to use as a punch or drift, they chip and break like a hard drill bit. At both places the both the pins and cotter pins were in the same drawer. The assortment of parts from both places ranged from the early 1900's to the early 70's.