The older Kleins had the pressed in bottom bracket cartridge bearings. Much like motorcycle wheel bearings. Not a big deal to replace if needed, but the bearings used are very high quality and last an extremely long time, even with heavy use.
The older Kleins do, however, use standard headsets. At least not the top of the line models. Mine is a Quantum Race, the lowest spec'd of the three Quantums available, and it has a totally normal Shimano 105-SC 1" threaded headset.
My 2001 Klein Adept Comp uses both conventional threaded bottom bracket and threadless headset in the now common size of 1 1/8". That was well into Trek ownership and that frame in particular was the same as the contemporary Trek Fuel and almost the same as the Gary Fisher Sugar as Trek also owns Fisher. So, it would make sense to have the Klein use more conventional parts.
Last edited by Pantah; 09-10-21 at 09:41 AM.