These 3½"pitons were among last weekend's auction plunder. I have a suspicion, but I really don't know. Make? Years?
Steve they look like Chev 6 cyl.1937 to 1942 approx.
3.500 bore Compression distance is 2.230 # C992F from the Thompson Toledo catalogue. (Check pin center line to top should be 2.230)
Best I remember 40 chevy and back were domed.KGB