A valve adjustment tool what's it

[bonneyman]

Can't remember if I asked about this tool or not. Just uncovered it again in my car tools box. Says RAP 612 on it, nothing else. Nicely made, not chromed, about 5.5 inches long, hex opening looks to be about 13/32" (but could be 10 mm- I didn't think to check it against a bolt).
Any ideas?

[lostmind]

I think it's a rear band a rear band adjusting tool for automatic trans. Probably Ford if it's 13/16
Could be GM hydramatic?

[Cruiser808]

This is what I use to adjust the FJ40. It’s got solid lifters, so this tool, as old as it is, gets used and is stored in the main box. I just hope I don’t break or lose it.

[J.A.F.E.]

I have a similar one I use for the Spitfire.