Williams flex adapter?

[earthmover1980]

I have a Williams flex adapter ST40 that I aquired at a sale. It was strange how it was machined on the female end. It is setup for a extension to plug in, but the female end is not machined to allow just any extension to plug in due to the radius's. Why would this be? What is it used for? I've never seen one like it. Why would the square female side not be machined with radiused corners?

 

[3baygarage]

The bottom was cut off by a previous owner. It’s unfortunate because that is a nice tool. It would normally taper down and accept any extension. I’ll try and find a pic.

 

[3baygarage]

It’s a part of the multi purpose set.

Some I picked up a while back.

https://www.garagejournal.com/forum/showpost.php?p=5185643&postcount=5541

 

[earthmover1980]

That's nothing like I expected!!! I didn't know that the thing was modified. Thanks for the help!