Pentax made two types of lens hoods for the 50mm standard lens, a round plastic hood and a rectangular plastic hood. They were designed when the lenses were used for film. With the current 1.5x crop factor where the 50mm lens is now an equivalent 75mm on film, one can go for a slightly deeper hood without the risk of vignetting.
The Pentax rectangular hood is a clip-on design. It is trick looking but not so practical as one can't use a lens cap over it. It also is overpriced for essentially something made of plastic, imo.
The Pentax screw-in round plastic hood is more practical because it is possible to use a clip-on lens cap (52mm) over it. It is also not cheap. There are of course 3rd party lens round hoods that are made of metal or plastic that offers similar function as well.