The K flat wagons have a heritage back to 1859. The class numbers were 1 to 486. They were built as required, with conversions from cut down wagons in the 1920's.
With the removal of hook couplings from stock in the 1950's, many K trucks were not suitable for autocoupler conversion. Seventy wagons were converted from autocoupled _IA_ wagons in 1953. These wagons were numbered 1 - 70. The few existing K trucks still running with low numbers were renumbered out of the way.
As well as flat wagon service, K trucks were modified for various uses. Some wagons were fitted with square tanks for use as water transports, later oil transport. Some were modified for crane use: cast iron turntable deck suitable for swivelling cranes of about 5 ton capacity. These cranes were uses for light duties at locomotive and maintenance depots.