That's a type of valve spring compressor that would be used on an L-head (aka flathead) engine, like a Model A Ford or similar. The valves springs could be removed after the head and side cover was taken off. I may have had one way back when. I definitely know I've used one.
Could also be used on an OHV engine head, but designed for L-head engines.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.