Fruehauf used to build their own axles, suspensions and brakes. All
different from the Rockwell or Rockwell clone stuff used by the rest of
the trailer manufacturers. Had to get the parts from them, at their
prices, or from a few aftermarket parts suppliers. You want to keep
costs down, you buy equipment that has common parts that can be bought
from any truck dealer, not just the OEM dealer. Competition keeps
things within reason.
Applies to cars, too: buy some oddball import and be
captive to their prices.

Dan