An aluminium banjo bolt with a 3/8-24 thread and a 23mm length under the head. Banjo bolts are hollow through the centre with cross-drillings that feed fluid into the banjo eye, letting a line connect to a port at any rotational angle, which is why they are used at calipers, master cylinders, clutch cylinders and carburettor inlets. Alloy construction keeps weight down and the finish tidy, though it does mean torque must be applied with care because aluminium threads will not tolerate the kind of force a steel bolt shrugs off. Always fit a sealing washer on each side of the banjo eye and tighten to the correct figure rather than by feel.