Well, according to the 1939 Plomb catalogue it is a No. 2110 Grease Bar. I can't read the font on the catalogue so if you have one please fill it in for what it is used for.
This is what I can make out from the catalogue
? like opening affect to clear obstructions and ? coarse teeth to prevent slipping. 28" long.
For greasing leaf springs?
open up the leaf springs so you could slop some grease in between so they didn't squeak as bad.
Here you go.......from the '40 cat.
I've had one for about 35 years ( not Plomb ). Use it as my go to pry bar. Just the right length.