Lightweight, durable aluminum back plate with upper guide and lower roller to keep chain on in extreme terrain. P40: 3/8" polycarbonate bashguard, guide adjustment to fit 36-40t, 260g. P30: 3/8" polycarbonate bashguard, FIXED (N/A) guide fits 36t ONLY, 230g. P20: 3/8" polycarbonate bashguard, guide adjustment to fit 32-34t, 215g. G45: 1/8" aluminum bashguard, guide adjustment to fit 36-40t, 245g. G25: 1/8" aluminum bashguard, guide adjustment to fit 32-34t, 195g.