Of a common were built during the 1960s and differed only in their centre heights. Not even the beds were altered, all being 450 mm wide and, in a fashion common to many TOS lathes, cut away in front of the headstock to form a shallow gap 300 mm long. Also following TOS practice were the model designations, these indicating swings of, respectively, 550, 630 and 710 mm. Five different between-centres capacities were offered; 1500, 2000, 2500, 3000 and 400 mm 
Other than the previously-mentioned differences in capacity, the threes lathes shared the same headstock with a 62 mm bore spindle fitted with CSN 20-011 nose (a short taper and bayonet quick-change fitting) and running in an adjustable two-row roller bearing at the front and a pair of ball races at the rear. 16 spindle speed were available from 99 to 1000 r.p.m driven by a 7.5 kW motor. The spindle speeds were arranged in two groups, a low-speed one from 10 to 112 r.p.m. and a high speed from 90 to 1000 r.p.m.
Over the full range of spindle speeds longitudinal rates of carriage feed varied from 0.05 to 0.8 mm/rev and in the slow range from 0.64 to 6.4 mm/rev. Cross feeds were set at half the longitudinal rate in both the high and low spindle speeds
Screwcutting was arranged to provide 29 metric pitches from 0.5  to 40 mm, 35 English pitches from 1 to 80 t.p.i., 26 module from 2 to 72 and 31 Diametral from 2 to 72 t.p.i.
Equipped with a large No. 5 Morse taper, the tailstock spindle was 90 mm in diameter with a travel of 240 mm
The shortest bed SN55 weighed approximately 2760 kg and the SN71 with the longest bed around 3500 kg. A detailed specification of the three lathes - and details of the various options and accessories available - can be found below..