Wolf Tooth Crown Race Adapters allow the use of forks with 1 1/8" or 1 1/4" steerer tube diameters in headsets designed for 1 1/2" steerer tubes. Many dual-crown suspensions forks such as the RockShox Boxxer or Fox 40 use non-tapered 1 1/8" steerers, and require a 1 1/8" to 1 1/2" adapter crown race for use in frames designed for a tapered steerer. Some road, CX, and bikepacking forks have 1 1/4" lower steerer tube diameters that would require an adapter to use a headset with a 1 1/2" lower headset cup.