This is a genuine Lucas - empty battery box of the large rubber (B38-6) type - which is the type of 6v battery originally fitted to a number of british bikes of the 40's/50's/60's - including both Norton and Vincent singles. It was also not unusual to fit this type of battery to Norton singles of the 1930's, as a replacement for earlier T-Shape batteries which were discontinued after WWII.
This empty battery box is a modern (hard rubber) replica of the original Lucas type (but still manfactured by Lucas), but does not have any battery inside it - instead it is ready to take a modern 'gell cell' battery. In the 3rd and 4th photograph I show one of those modern dry cell batteries (not included) - which will fit snugly in the case.
Its dimensions are as follows:
Internal drop (i.e how high from base to lip of main case body): 133mm. Internal width x depth : 104mm x 76.5mm.
External dimensions (which should be standard battery case size for this type of original 6V Battery, as fitted to most 1930’s – mid 50’s Norton singles : 160mm Height x 115mm width x 89.5mm depth.