This might be the most important training aid you ever make and practice with for your whole swing.

 Great at training proper wrist and hand action, proper elbow folding both in the backswing and follow through getting rid of your slice, great at helping you feel a natural weight shift, and great at helping you feel a unified tempo to your whole swing. 

I didn't realize how important it is until I recently did several lessons using my Big Black Club you see pictured below. I had a student in a lesson continuing to flip his wrists and hands at impact and I was at a lost to find a way to get his hand and wrists to calm down and move in a natural unguided non controlling way . 

I had him do small half swings with the large headed plastic driver feeling how the weight and size of the club took him and his hands and wrists through the correct positions without him having to manipulate the club or do anything. After maybe 10 to 15 half swings with the larger club I switched him to a regular club ( 7 iron) and asked him to make half shots now. The resulting shots were magical. And dead straight with little to no effort. He was shocked and very happy. He had just learned how to hit a ball straight!

Over the course of the next weeks lessons I heavily taught using the Big Club to help my students feel how their hands should work .. many for the first time .. and realized just how important this is and how I had taken it for granted as it is something my hands had just learned to do over time. 

I started to look at other training aids in an effort to find an easy way for all students of mine to learn this feeling quickly. 

The additional weight extended teaches your hands and wrists to rehinge at the proper time. The feeling I get is also a sensation of the shaft snapping back just past impact . Its not a forced feeling though. It trains your hands and muscles to know what a good golf swing feels like. When your hands know what to expect they allow it to happen properly and don't fight it. Your just letting it teach you.

Training Aid background .. why is this so important ?  Existing Training Aids 

Sadly no available anymore but when I bought it was $120 15 years ago

I bought mine on Kijiji for $60 but you can still but them for about $100 US

Not available or just way too expensive to ask my students to go out and get one ..Would I be able to make a training aid that would create this same feeling of rotational force ? 

How to Make Your Own Swing Bar ( Safely)