Tooling: Reducing the Mass In Sprue Bushings
d) The head of the bushing should be supported by at least 3/8 in. of moldbase steel for small molds and 5/8 in. of moldbase steel for large molds. Internal Taper : Back in the 1800s, the Brown and Sharpe Co. invented a taper with an included angle of 1⁄2 in./ft for end mills, collets, and machinetool spindles.