LEICA FILCA 35mm Film Cassette Leitz Germany + Original Metal Pot. (ref1)
This is a FILCA 35mm film cassette as opposed to a IXMOO.
The FILCA is taller and has a black knob on top unlike the IXMOO which is chromed.
It only fits the pre Leica M3 series cameras with screw mount lenses such as the Leica IIIc.
Screw mount bodies can take either the FILCA or IXMOO but M bodies can only use the IXMOO.
The FILCA is the older than the IXMOO and does not have the Leitz name printed on the base.