1. This pair of hex wideners is having a total width of 23mm to achieve a wider wheel distance for stabilization. 2. This pair of hex wideners is having 4mm hole that can be compatible with a lot of other models as long as the sizes are fit. 3. There are o-ring on one side and spring steel ring, spring with washers, stainless steel screw on the other side to tighten the hex wideners from loose out with a special delrin collar inserted inside to secure the hex in position so that the wheels and tires are not going to spin around, especially during the crawling track that your Axial SCX-10 II can face a lot of traction. This product includes :