I picked up an old oak office chair from a neighbors garbage. It was the victim of many botched repairs. In one case, a steam bent half round arm had split and had been repaired with a bolt with a peculiar curved head like the ones shown below. All I could find are some vague statements about the bolts being used to hold chair legs.
B5C2D79C-7CBA-472A-8D21-77DBE9890D4C.jpeg
Anyone know more?