MK0 items represent a refined approach to component engineering with special consultation with Team Visma Lease A Bike. Each top cap spends 4x more time in Wolf Tooth's CNC lathe before undergoing thorough QC inspection and anodizing in the new Shadow Gray color. The extra machining and new profile of the MK0 upper headsets have meaningful gains and result in a 44% reduction in aluminum weight without compromising strength and durability. These super slammed 4mm stack upper headsets feature extraordinary sealing to prevent water intrusion and provide protection for the premium Enduro stainless steel sealed bearings.MK0 IS upper headset feature a super low 4mm of stack made possible by the extra machining and new profile that result in a 44% reduction in aluminum weight without compromising strength and durabilityO-ring seal prevents water intrusion around steerer tube to eliminate corrosion that results in longevity of the headsetCustom-molded upper lip seal provides additional protection for the premium Enduro stainless steel upper 36 x 45 degree beveled angle bearing Ships with a star nut which can only be used on forks with steel or aluminum steerer tubes (Carbon steerer tubes require a compression plug and are sold separately)MK0 IS upper headset includes stem cap custom hollow bolt starnut and Enduro stainless steel sealed bearings