This is a set of ProBuildT 1.9" Brass Center Ring with Lead Weights, which makes it easy and accurately adjust and distribute the weight on beadlock wheels.
A standard ProBuild wheel weighs about 73 grams (2.57oz). Adding this full Brass Center Ring can double, triple, and quadruple the total weight - up to 272 grams (9.6oz) per wheel.
The original weighted ring was made when even experienced RC builders found it impossible to adjust their beadlock wheel weights precisely and wanted a robust system to do so. The Brass Center Ring system allows you to do just that - adjust the weight of your beadlock wheels precisely.