Britannia 6" x 42" gap-bed, backgeared, screwcutting No. 17 lathe - the first in the company's range that was considered too large to be offered on a treadle stand. This was a substantial machine that, despite its slender appearance, weighed over 13.5 cwt. Just one centre height was offered, of 6 inches and, whilst a 6 foot long bed admitting 42 inches between centres was standard, beds of any length could be supplied for an extra charge of £2 per foot.
The design of the lathe closely followed that of the Nos. 15 and 16 machines but the bed - 8.75 inches wide, 6 inches deep and with a 10-inch long and 6-inch deep gap was very much more heavily constructed.
Included in the price of £44 : 2s : 0d was power sliding and surfacing by a "backshaft", a 4-speed fast-and-loose countershaft assembly, 22 changewheels for screwcutting, a faceplate, catchplate, index plate, spanners and centres.

Britannia Lathe Nos. 18 and 19 of 5-inch and 6-inch centre heights respectively. This was a special lathe whose origins can be traced back to a British Admiralty requirement for a self-contained lathe, suitable for shipboard use, that could take heavier-than normal cuts under treadle power alone and remove 1/2" off a 2" or 3" bar in one pass. This was achieved by building a second backgear assembly above the headstock spindle line - and meshing it with the normal one at the back. This was a system that Britannia - and many other makers, but not all - referred to a "Treble Gearing". The argument for using the term "Treble-geared" was based on the premise that a headstock driven directly by a belt was normally referred to as "single-geared" and with an ordinary backgear "double-geared" - hence, with a second backgear it must be treble-geared. As advertising hyperbole it certainly sounded impressive - even if it was untrue. Some lathes (but non by Britannia) did had a genuine treble-reduction headstock spindle assembly -  the final drive from the second backgear being to a gear formed on the inside rim of the faceplate. The American Hamilton lathe, seen here, was one such machine.
Besides it ability to remove metal quickly, the lathe was also able to swing 24 inches in the gap and, because of its ultra-low spindle gearing, would almost certainly have been able to use this facility to the full. In other respects the design of the lathe, and its equipment, were much like other Britannia models with tumble reverse, no graduations on the compound slide feed screws and solid headstock spindle. Supplied as standard with the lathe were 22 cast-finish changewheels, a faceplate and catchplate, two centres, spanners and a back (travelling) steady whilst the options list included a set-over tailstock and power sliding and surfacing from a "backshaft"

Britannia lathes Nos. 21, 22 and 23; these were the largest examples advertised by the company - although bigger ones were made to special order; whilst all three were almost identical in appearance, their physical construction was sufficiently different to render each a special machine in its own right - there being very few interchangeable parts between them. The centre heights were, respectively: 10 inches, 12 inches and 14 inches, the bed widths 16 inches, 19 inches and 23 inches, the bed depths 11 inches, 13 inches and 14.5 inches, the bed lengths 12 feet, 12 feet and 20 feet, the capacity between centres 7ft 3 ins, 6 ft. 8 ins and 13 ft 6 ins - and their masses (they were no lightweights) 2.5 tons, 4 tons and 5 tons, with basic equipment.
In order to support the huge bed, the left-hand end of the machine was cast with a massive, integral foot; however, this must have been greatly weakened by the large gap cut into it that offered, in centre-height order, the ability to turn discs up to: 41 inches, 49 inches and 57 inches in diameter.