The K sets are a class of electric multiple units (EMU) that currently operate on the Sydney Trains suburban network.

The carriages are of stainless steel, double deck construction and share much of their design with the older S sets.

Two orders were placed for the K sets with all manufactured between 1981 and 1985 by A Goninan & Co in Broadmeadow: The first order featured low mounted upper deck windows, off-white and sagebrush grey interiors, and unpainted fronts, though at least one had its front painted in State Rail Authority candy livery (see picture to the left).

The second order featured higher mounted upper deck windows, yellow and mustard interiors and State Rail Authority candy livery fronts.

Although some power cars and trailers have been broken up and married with others during periods of heavy maintenance, many original combinations remain.

The guard uses the area outside of the driver's compartment, with two manual hinged doors on either side providing access to platforms.

With the trials on the ten experimental carriages judged successful, in 1986 a programme commenced to retrofit air conditioning to the second order.

[6] In April 1989, K sets commenced operating peak-hour services via the North Shore line to Gosford.

[9][10] In January 1991, four sets were transferred to Flemington Maintenance Depot to operate peak-hour Illawarra line services to Port Kembla.

These cars retained the hopper windows until the late 2000s, but were sealed shut with an adhesive to avoid the loss of air conditioning.

In mid-2014, K sets were gradually transferred from Hornsby to Flemington resulting in their resumption of service on the Airport, Inner West & South, Bankstown, Carlingford and Olympic Park lines.

Also, unlike converted S set cars, the round window on the crew compartment doors were removed and covered with a metal plate.

In July 2017, asbestos was found in the circuit breaker panels, which is inside the driver compartment of the K sets, with all withdrawn for inspection for a few weeks.

In 2019, set K96 was withdrawn from passenger service and had Automatic Train Protection (ATP) equipment installed.

It featured a mix of classic and purpose-written music by Mac to accompany the train on its journey, with occasional commentary included.