This brass back plate is a replacement for the YD-2Z gear case cap to increase weight and rear traction. Compared to the standard part (5g), the brass backplate (31.8g) adds a significant amount of weight, especially on P-tile and colored concrete surfaces. In addition, the RTC (Rear Toe Control), which is available for YD-2S, can now be used together, greatly expanding the range of settings for the rear area.