Some short axle to axle bow users were noticing a small thump when using the previous STS model. In order to rectify that problem, we have created the double STS archery system. The double STS archery system mounts to the front or the rear of the riser depending on the model used, and utilizes two STS stoppers to dampen noise and vibration. It also works great on longer axle to axle bows. COLOR: REALTREE HD GREEN