First offered during the 1970s, the TOS SU1-40 and SUI-50 were of identical design, mechanical construction and specification and shared a hardened and ground bed some 360 mm wide. Like many TOS lathes, the model name was derived from the centre height in mm, these being, respectively, 400 and 500 mm. To allow a little more capacity, the bed ways were cut away as they approached the headstock, this modification giving the SUI-40 a maximum swing of 460 mm and the SUI-50 560 mm with the workpiece limited to a depth of 300 mm
Three between-centres capacities were available - 750, 1000, 1500 and 2000 mm - with all versions able to take a workpiece between centres weighing up to 400 kg between centres - or up to 480 kg when supported by a fixed steady.
All versions shared the same 56 mm spindle bore and had 42 rates of longitudinal carriage feed from 0.023 to 4.9 mm per rev and the same number in traverse from 0.011 to 2.4 mm per rev. For the UK market (and probably others but not all) rapids on both directions of feed were an option (operated by a push-button at the top left-hand front face of the apron). Rapids were driven by separate apron-mounted 0.55 kW motor that gave rates of 3600 mm/min longitudinally and 1750 mm/min in traverse.
Screwcutting differed according to the year of production with lathes made in the 1970s arranged to provide 55 metric pitches from 0.25 to 60 mm, 72 Whitworth (inch) English pitches 0.5 to 120 t.p.i., 32 module form 0,125 to 15 and 56 DP from 2 to 240. Unaccountably, later models had a reduced number of metric and  Whitworth pitches, these being 45 metric from 0.25 to 60 mm and 64 Whitworth from 0.5 to 120 t.p.i. - though the number and range of module and DP remained unchanged.
Driven by a 7.5 kW, 1400 r.p.m motor and driving through a multi-disc clutch and a pre-selector gearbox, the 18 spindle speeds offered as standard ran from 14 to 2240 r.p.m.  As an extra-cost option - as with many TOS machine tools  -both faster and slower ranges could be specified.
The full specification - and details of the various options - can be found below..