Cast aluminum, 4.730 in. Min, 4.733 in. Max dia, 4.000 in. Lg, 3.520 in. Min, 3.524 in. Max diameter of front end opening, 2 holes-no. 29 drill and tap no.8-32 unc 2b located 0.188 in. On each side of vertical center line on 4.000 in. Diameter bolt circle