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A banjo fitting (also called an internally relieved bolt) comprises a perforated hollow bolt and spherical union for fluid transfer. They are commonly found in automotive fuel, oil and hydraulic systems (e.g.: brakes and clutch). The pipe connected may be either rigid or a flexible hose.
The main advantage of the fitting is in high pressure applications (i.e. more than 50 bar). The name stems from the shape of the fitting, having a large circular section connected to a thinner pipe, generally similar to the shape of a banjo.
Compared to pipe fittings that are themselves threaded, banjo fittings have the advantage that they do not have to be rotated relative to the host fitting. This avoids risk of damage by twisting the hose when screwing the fitting into place. It also allows the pipe exit direction to be adjusted relative to the fitting, then the bolt tightened independently.