Needed a M18 holder that was lockable and no supports needed. Also I only wanted 2 screws and not 4 like most I found. Couldn't find one I liked so I deisgned this one.
I have designed 2 of them. One for a countersunk screw and the other for a flat head. I prefer flat as it has less chance of spliting the plastic but other people may want the countersunk version.
Enjoy
PS. Check out my profile for other trade related models.