Bearing surface materials do not have to be of equal hardness. Soft materials can, in fact, work just fine if of proper design and lubrication. Soft on hard brings up the issue of grit embedment in the soft material. Hard on hard is best, provided the fitting is well done. Hardened and tempered plain high carbon steel makes a mighty fine bearing surface.

Did Parker use any special steel alloys for hinge pins of hooks? Those show wear far mor often than do locking bolts and lump bites.