A similar rotational bearing comprised of a rotating arc or ring sliding in the groove of a stationary arc, used in machinery to allow a workpiece to be moved relative to a fixed tool
Twin cylindrical projections, cast as part of a gun tube and projecting to left and right at right angles to the bore, slightly forward of the center of gravity The trunnions supported the weight of the guns as it rested on its carriage, and the piece pivoted on them as it was raised or lowered in elevation Placing trunnions forward of the center of balance (4/7 of the distance from breech to muzzle was an 18th-century rule of thumb) placed the preponderance of tube weight at the breech end and kept the piece stable when fired