What do "H" and "B" stand for in the naming convention for each model?

Usually, "H" means a handheld mic, while "B" means a bodypack for Phenyx Pro wireless systems. PTU-52-2H means a PTU-52 system with two handheld mics. PTU-52-1H1B means a PTU-52 system with one handheld mic and one bodypack.