Banjo Bolts for Brake Calipers & Master Cylinders The Right Bolt for a Leak-Free Hydraulic Connection
A banjo bolt is the threaded fastener that secures a brake hose or hard line to a caliper, master cylinder, or ABS unit. It passes through the hollow eye of a banjo fitting, threads directly into the port, and clamps two copper sealing washers against the mating surfaces to form a sealed hydraulic connection.
How to Identify Your Banjo Bolt Size
Measure three things off the old bolt: thread diameter (e.g. 10mm or 3/8"), thread pitch (threads per inch for SAE, mm between threads for metric — a thread gauge makes this foolproof), and shank length. Common brake sizes: M10x1.0 and M10x1.5 (most Asian/European calipers), M12x1.0, 3/8"-24 and 7/16"-24 (American), 1/2"-20. Every product page lists all three measurements.
Installation Tips for a Leak-Free Seal
Always use new copper crush washers on both sides of the banjo fitting — they work-harden and won't reseal once compressed. Thread the bolt by hand first, torque to your vehicle's spec (typically 25–35 ft-lbs for M10 caliper bolts — verify in your service manual), and bleed the brakes afterward. Never wrap banjo bolt threads with PTFE tape; the seal is at the washers, not the threads.
FAQ
Are banjo bolts universal?
No — thread diameter, pitch, and length must all match your caliper or master cylinder port. An M10x1.0 will start in an M10x1.5 port but will strip it.
Can I reuse copper washers?
Not reliably. They're a few cents each — replace them every time the joint is opened.
Why is my banjo fitting still leaking?
Usually reused washers, a scored sealing surface, or under-torque. Clean both faces, fit new washers, and re-torque.
