For mooring steamers of about 900 tons, the concrete block for the mooring posts or bollards should be not less than 7ft. 6 in. square and 8 ft. deep, with a block of Bramley Fall stone 5ft. square and 1ft. 6in. thick on top. The part of the bollard above the ground line is usually a separate casting, securely bolted to the foundation column, which is bedded in the concrete, with a flange at the bottom bolted to two 12-in. by 12-in. baulks of creosoted memel. The shape of the upper casting varies from a post with rounded head and hollowed side, or a capstan-head shape, to a tall or short hook shape. The thickness of metal is about 1 3/4 in., tapering to 1 in. at the bottom of the concrete. The diameter where the rope goes is about 18 in., and the bottom end l5 in. The engineer of the dock usually gives the design both for the bollard and the foundation, as every part must be calculated to do its duty efficiently.