ST1 Upgrade Disc - High torque sprung disc assembly lined with a heavy duty steelback organic friction material. By riveting "steel to steel" M-Pact's advanced steel back friction material provides additional clamping force and superior burst strength. The reinforced steel backing allows for better heat dissipation delivering extended wear and quick recovery. The M-Pact ST1 disc is assembled using precision engineered components designed for slight increased horse power applications. Each disc is assembled with a HD retainer stamping and increased hardness hub to ensure maximum strength and reliability. Six inner and six outer heavy duty torsional dampening springs work with this assembly to ensure a smoother engagement.