Prestacycle UniBlock Cassettes are a single-piece unit exquisitely machined from a solid block of cold-forged Chrome Molybdenum alloy steel, then heat-treated, tumble-finished and electroplated for added durability and low-friction operation. The 2 largest cogs on the 11-40 and 11-42 HG11 cassettes are crafted with one-piece of high quality 7075 aluminum.