The only stock affected in this recoding were the _I__ wagons. With the large influx of 16 to 27 ton wagons through the 1920's, the railways began to scrap the 8, 10 and 11 ton wagons from 1927. This led to a supply problem of smaller capacity trucks which had accounted for about 6000 wagons.
The primary industry objected to cartage fees for small items being carried at 16 ton wagon rates when an 11 ton vehicle had been ordered. This had been initially raised as early as 1908 with introduction of the longer 16 ton I open wagons ( ie non 'Tommy Bent'). It seems interesting that a simple logistical fix it took about twenty years to solve the problem. A dual capacity code was introduced during 1928 and was the _IA_. This wagon had a dual capacity of 11/16 ton. This meant that loads up to 11 ton were carried at '11 ton rate' and loads over 11 ton and up to 16 ton were carried at '16 ton rate'.
As early as 1926 I wagons were in service with the dual tonnage lettering.
At 1928, 16 ton I wagons would be recoded to IA on a one-for-one basis as 11 ton I were scrapped. The 11ton to 16ton wagon ratio was enforced until the 1960's. It even transpired that too many IA wagons were converted at times and were required to be recoded back to I.
Through the 1930's, conversions were at the rate of about 20 a month. The official 'Registers' do not record the actual I to IA conversion dates. Some wagons are recorded as I to IA to I and again to IA.
In this same recoding, the 11 ton I wagons were designated as _IB_.
The 16 ton drop door wagons coded _IG_ were recoded to I.
File m1929m compiled by Peter J. Vincent, updated 27/3/2008