When I first held one of these in my hands I did not have a clue what it was. I played with it for a number of minutes trying to figure it out. I assumed it was a block off cord but simply was bewildered on how it worked. In frustration I grabbed the threaded cord and just pulled on it and the block came off in my hand! I was still bewildered as I had now idea how this miracle just happened. Closest thing to magic that you can feel is to fool yourself.
This is a mechanical masterpiece with a lot going on within the block. You will love it. In excellent condition. Block is 3 inches square.