What kind of a nut does this remove

[Shade guy]

What kind of a nut does this remove

 

[BFBOB]

A BIG one!

Looks shop-made to me, to reach a nut that's recessed; maybe a locknut on a pin on heavy equipment? Front loader/excavator arm or the like?

 

[lis2323]

Most likely for removing a “spline head” bolt for wheel lugs.


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[gatlibs]

See how the second image is a round base for the castellated nut cover? I'm guessing a round based castellated nut.
https://en.m.wikipedia.org/wiki/Castellated_nut

 

[Jbullfrog]

Based on the length of the handle, I would say a spindle nut within a hub. Gatlibs's link shows a tin castellated lock cover, on a 12 point spindle nut. This wrench would be used to turn the nut after you removed the locking cover.

 

[KnurledNut]

It would have to be a low torque application, as the bi-hex is only plate steel. 1/4"?
What is the dimension across the flats?
Definitely looks shop made for a specific application, perhaps industrial or heavy maintenance.

 

[Shade guy]

It is 1/4 plate and it's 2-1/2 inches across the flats