The OBA, OCA, & SPA wagons followed the OAA wagons, to form the largest part of the air braked open wagon fleet. They have similar underframes and suspension. There were 1600 SPA wagons,
a large number of which were transferred to the engineers' fleet (ZAA - PIKE).
This was also the case with the OBA & OCA, as about half the 800 OBA's and some of the OCA's were coded ZDA - BASS.
However, after being taken over by EWS, most if not all of these wagons returned to revenue stock, although they were still used for engineering work. Some OBA wagons were rebuilt as "Sea Urchin" wagons and 30 OCA wagons had new fixed sides as "Seahorse" - see the Departmental page for kits.
The kits have pivotting wheel/axleguard units which are turned by the couplings, and returned to a straight position by a tension spring.

C17 OBA 31tonne WOOD BODIED OPEN WAGON (1977-9)
The kit has the body style of the second half of the build, with unequal spacing of door hinges and straps, plus square door "buffers" rather than round. The Bachmann RTR version has the earlier type of body, although the numbers applied to these do not necessarily take this into account.

C18 OCA 31tonne STEEL BODIED OPEN WAGON(1981-2)

C19 SPA 31.5tonne STEEL PLATE WAGON (1980)

These have a distinctive chequer-plate floor and wooden cross battens. The solebar is shallower without the cut outs found on the OBA & OCA. The lower picture shows a ZDA Pike in the "Dutch" livery — later on some of the Pikes had the doors welded shut and became "Seahares"
Some had a row of stanchions down the centre and a locker at one end.
Others were fitted with a blue pvc hood. A number of wagons were were converted to "Sea Urchin" wagons with fixed sides for ballast and spoil.
Timber wagon conversions:
125 of the OCA wagons were converted in 1985 to OTA timber wagons. They are used to carry softwood to paper mills. Seen mainly in the South West, Wales, the North & Scotland. The number of locations served was reduced after the end of the Speedlink service.
C20 OTA(A) 46tonne GLW TIMBER WAGON (1985)

OTA(A)'s had either 11 or 13 stanchion sockets; either of which can be made from the kit.
More recently some of the stanchions & sockets have been removed leaving only 8 on each side.
Includes a capping strip for making the flat-topped-end version, as shown below.
C21 OTA(C) 46tonne GLW TIMBER WAGON (1985)

This type had 9 stanchions. There were 25, originally leased to Thames Board to take timber to their Workington Mill, but when this traffic ended, they went back into the pool of OTA's. Some retained their blue livery for some years afterwards.