Die-cast from aluminum alloy to help dissipate heat, resist breaking, warping and cracking. Trailer hub cap Includes oil window, 1 standard vent plug & 1 ESP (Extended Service Plug), side pipe fill plug and gasket, mounting bolts not included. Bolt holes = 6, bolt circle = 5 1/2”, bolt hole size = 5/16”, fit = Trailer. Approximate dimensions = flange OD 6 1/4″ flange ID 4 3/8″ height 2 11/16″. Replaces: Stemco️#348-4009 SKF️#1643