Featuring some of the lowest stack height bearing cover options available, the Cane Creek Hellbender 70 Slam SHIS - IS41 4.6mm - Upper Only is a premium headset designed for riders who want to lower their handlebars as much as possible without compromising the lifespan of the bearings or proper preload.The cups and covers of this headset are made from 6061 T-6 Aluminum, which not only minimizes weight but also maximizes strength. The top cover is designed to have the lowest stack height possible for both ZS and IS headsets. The alloy Dual-Seal crown race provides excellent seal efficiency, while the low friction Carbon friendly captured compression ring ensures smooth operation. The premium sealed HELLBENDER stainless bearings offer exceptional performance and longevity.The stack height for ZS headsets is 2mm on top compared to 8mm for a regular ZS Hellbender, and for IS headsets, it is 4.6mm on top compared to 9mm for a regular ZS Hellbender.If you're looking to upgrade your headset to a high-quality option that allows you to lower your handlebars while maintaining optimal performance, the Cane Creek Hellbender 70 Slam SHIS - IS41 4.6mm - Upper Only is the perfect choice.