The GZ wagons were basically a grain proofed version of the _IZ_ wagons then under construction. The first GZ wagons were issued to traffic on 5th July 1935 and were numbered 1000, 1001 ( part of the IZ number group ). For about three months prior to this, eighty two IZ wagons were released to traffic built for "bulk grain" traffic.
With the introduction of the GZ code, the 'wheat proofed' IZ wagons were recoded to GZ. As a result the final GZ number group became 911 - 1030, 1100 - 2000.
With large numbers of _GY_ wagons in service by the mid 1950's, the GZ's were progressively withdrawn from bulk grain traffic and placed in general service as IZ wagons.
In 1959, IZ 58 was modified with high sides for carrying oats and coded GZ 58. The wagon was rebuilt to standard form in 1961 when the wagon became HZ 58. Of interest, the high doors survived and were found in the 1970's fitted to a _HD_ service vehicle.