All trams of this type were built by the Finnish metal industry corporation Valmet between the years 1973 and 1975.

[1] As the first mass-produced tram type in the world, the Nr I featured thyristor chopper control.

Instead of the traditional green/yellow colours, the new trams were painted light grey, with an orange stripes running along the top and bottom of the carriage.

The livery was identical with the standard green/yellow colours, but had an additional narrow yellow stripe running along the bottom of the carriage.

[1][2] Following the 1993–2004 modernisation process, HKL officially gives the seating capacity of all units as 39, with 106 standing places.

[4] Originally the seats of the Nr I class were covered beige-coloured artificial leather upholstery.

[11] The Nr II class trams have been fitted with a low-floor midsection from 2006 onwards,[12] and fitting the Nr I class units with similar midsections to increase their lifespan is also reported to be under consideration (as of June 2008).