Anybody know what this is?

[lolaetype]

Rest assured I don't.

 

[cvairwerks]

Old style rocker arm adjuster?

 

[KnurledNut]

https://patents.google.com/patent/US2704474A/en

 

[DAWrench]

Well I feel educated now. Have a tool like that in a junk box and never knew what it was. I kept it just in case I might need it someday...for something