In my experience Leitz had different lenghts on same diametre lensmounts, so some would not go far enough in towards the dias even though they would fit the lens opening. THe ones marked P2 would fit the big "battleship" projecctors. I also found that a Zeiss P-planar would fit (presumably made for the Zeiss projectors at the Zett werke that leitz later bought to make their much less heavy projetors)

p.