This is 6-1/4" long. 3/4" diameter turned down to 3/8" diameter. The ears are 1/16" wide. Was full of crud when I got it and washed off nice. Any ideas?

Screw  starter ?

reminds me of a split saw screw driver; something like this:  https://toolsforworkingwood.com/store/item/GT-SPLIT.XX

It could be a carb tool. Sometimes jets use a similar driver.

I like your original post, could be a key for a lathe chuck!!

I'm with J.A.F.E. on this one. I had a Proto like that that I got back in the very early '60's. Never did use it. A screwdriver worked just as well.

Mike