The Duncan silver MOD Spacers kit 5156PK included a long axle screw, two metal bearing spacers, and two plastic MOD Spacers. The MOD Spacers used recessed silicone response pads for the response. Because this kit does not come with a bearing like the Duncan MOD Spacer kit model 5158PK, you must use the bearing that already comes with your yo-yo.
The kit let you change your yo-yo from one intended for looping (narrow string gap) to one that is shaped best for string tricks (wider string gap).
The Hasbro Morph Master solved the issue of having to disassemble your yo-yo and keep track of parts like those from this kit. The Morph Master used a unique patented system that let you configure the yo-yo for looping or string tricks simply by reversing the halves and clicking them back into place.