Bleeder valves and banjo bolts share a similar construction and job in your braking system. Both are drilled to allow fluid to flow through them. A banjo bolt (bottom) allows fluid from a machined block attached to a flexible brake hose to enter a caliper. The bolt seals the block to itself and the caliper via sacrificial copper washers that get crushed as the banjo bolt is tightened. Bleeder valves (top) have a conical base that seals in a corresponding bevel in the caliper. When you bleed your brakes and “crack” or open the bleeder valve, this conical base breaks the seal with the caliper and allows air or brake fluid to leave the system.