AP calipers are rigid yet lightweight. They have a high quality aluminum alloy body with cast in protection for the bleeders and stainless steel cross over lines. The AP's have thin wall stainless steel pistons for low heat transfer from the pad. The feature that has most impressed us is the piston seals. They have endured incredible temperatures undamaged. The SC200 series calipers have all of the same features as the SC300, they just have a smaller casting to accommodate the smaller pistons.