Originally posted by UncleVanya JJC makes a copy that's cheap of the plastic hood.
Also I think...
PH=Plastic Hood
RH=Rubber Hood
And S = Square while R = Round (PH-S49 | PH-R49). The round plastic hood screws on, and there is also a metal screw on hood specified for the M50/1.4 = RH-R49 (probably the same as the metal hoods for m42 Takumar lenses, but it had a catalog number in the M lens era)
The naming convention above is fairly consistent across all the Pentax plastic hoods, with the variant being the thread diameter.