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This is the 8:31 ring and pinion set for Hewland and Webster Mk8 and Mk9 / Model 400 gearboxes. The ring gear uses the current 7/16" mounting bolts (some early Webster differentials were drilled for 3/8" bolts). Hewland part number HC8221A.
Setup Note: Hewland pinions are marked with the Clearance, to be measured between the head of the pinion gear and the Hewland setting jig. The Hewland setting jig measures 4.71" diameter and is centered at the axle centerline. Add 2.355 to the Clearance to find the distance from the axle centerline to the head of the pinion gear.