This is a very useful item, used for mounting baseless electric motors Frame 56C. New, updated design.
This type of motor comes without a mounting base, so it is quite a task to have it mounted. The solution is here.

This heavy duty mounting plate/bracket is made of 3/8" thick steel (or 5/16" sometimes)

Please note that the motor seen on the last 3 photos is not part of this listing. 

It is presented here as an example, helping to understand how the devise works.

The center-to-center distance between each of the four mounting holes is 4-5/32” or 106 mm.