This tool has 3/8" female square-holes on both ends.There is a circular hole all the way through both ends (I imagine this is to relieve air pressure, to aid in attachment).My use was to create a Double-Female-Ended socket extension (See photo).One ends 3/8" hole has a relief-detent on the inside edge to make it easier for the ball-bearing-lock to enter and engage. This is a tight tolerance hole and fit! The other end is a normal socket set type easy fit.Know the difference.Installing it on the tight-fit ball-bearing attachment end was not a hand fit! I had to use a light tap with a hammer on the other end to engage and seat it on the extension. The connection is solid and it will not be easily removed. It will probably take a slight hammer tap to remove it from this end. My use is permanent, so I am happy with this design.The end with the detent is tight, by design I think, so it will never easily fall off. The other end is a normal hand installed 3/8" socket connector. Easily added to and removed like normal socket ends.I have only one reservation. My use is light duty. I have not tried it with an impact wrench in hard daily use. It appears to be a stout and strong unit. But I make no claims or knowledge for tough usage.This is a well thought out, engineered and executed tool. I fully recommend it.
Rating: [5 of 5 Stars!]