20-MM ANTIAIRCRAFT GUN MOUNT
MARK 4 AND MARK 2
Part numbers of the Mark 4 parts are shown in the Mark 4 (OE.) column. Part numbers of the Mark 2 parts are shown in the Mark 2 (item) column.
Parts that are interchangeable between Mark 4 and Mark 2 have their Mark 4 (OE.) number and Mark 2 (item) number in the same line.
Parts of an assembly have their names indented under the assembly name.