The 40-Series sets the standard for performance, durability and value. Drawing from the Premium 110-Series Design, the 40-Series incorporates all the features necessary for a durable, light-weight, long-lasting headset. To make it easier, we developed consistent graphics, interchangeable parts and over 40 configurations to meet almost every need. Sold in straight and tapered assemblies or tops bottoms, Cane Creek's 40-Series offers the largest fitment range of any headset line on the market. Precision engineered by Cane Creek in Fletcher, NC. 6061-T6 alloy, Durable steel crown race, Black oxide cartridge bearings Innovative Clip Seal seals the top assembly and captures the compression ring for fewer loose parts 40.ZS49 BOTTOM, Bottom Type ZS ZeroStack, Bottom Head Tube Inside Dia. 49.61mm Crown Race Seat Dia. 30.015mm, Crown Race Type Steel, Face-Sealed Bottom Stack Height 4mm, Bottom Bearing Type Black Oxide, Sealed, Weight 58g