Maybe everyone knows this, but I recently found out that Hiduminium is a real thing, not just a GB (Gerry Burgess) marketing term. It's a high-tech (for back then) alloy with some impressive properties, developed by Rolls Royce for auto-racing engines, and later aircraft engines. It's short for High Duty Aluminium. Some of what makes it great may be moot for bike parts, such as retaining its high strength at high temperatures — more important in an IC engine piston than in a bicycle part. But notably stronger than the typical cr@p that lots of alloy bike parts were made from back then (or now?)

Snippet from the Wikipedia article: "In time, the post-war Reynolds company, already known for its steel bicycle frame tubes, would attempt to survive in the peacetime market by supplying Hiduminium alloy components for high-end aluminium bicycle cranks and brakes."

Good article here about GB Hiduminium brakes, by Hilary Stone