The Burroughs B4998 is the smallest Nixie tube ever mass produced, it's tiny elliptical envelope is only 15mm high and 10mm wide. The B4998 contains the same 8mm digits as the 4021L tube shown above, but the elliptical envelope reduces the overall size of the tube and allows for tighter side-by-side installation of multiple digit displays. B4998 nixie tubes are highly coveted among modern hobbyists for use in construction of 'Nixie watches' and other tiny Nixie displays.
Ironically, the integrated driver modules provided by Burroughs for use with the B4998 are much bulkier than those manufactured for it's larger tubes.