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Trek developed Knock Block as an integrated frame protection system to prevent self-inflicted scuffs, dents, or cracks from spinning handlebars. Knock Block consists of a special stem and a stop chip on the frame. The stop chip limits the turning range of the custom keyed headset cover. The top of the headset cover has notches that lock into corresponding notches on the headset spacers, which also correspond with notches in the stem for a strong connection to the steer tube. These parts work together to prevent the crown of the fork and handlebar controls from hitting the frame when bars are turned too far in either directio.
Compatible only with Trek Knock Block These spacers have unique raised features that key to Knock Block compatible stems (made by Bontrager) 1 1/8" top (straight 1 1/8" or 1 1/8" to 1 1/2" taper) steerer tubes only