This is the lock knob used to secure the red safety filter assembly in the lens stage of LPL, Saunders/LPL, and Omega/LPL 6600 and 6700 enlargers, and LPL 7700, and Saunders/LPL and Omega/LPL 670XL enlargers.
Please note that this is not the correct red filter securing screw for LPL 4x5 enlargers - see item #LPL3231-185.
