Not pictured but block is hollow with rubber coated metal core. This creates a durable last that doesn't slip with rubber ribs on both sides. However, this is also a weak point in the design, since my truck weighs 1600 kilos. A wedge was crushed on each rear wheel. I replaced it with Vestil LWC-15 durable laminated rubber. Vestil is heavier, but it won't fail, as will a hollow wedge. This is an excellent wedge for light vehicles even on steep surfaces. With a heavy vehicle on a steep surface I would use a solid wheel liner instead.