||Ex G.C., 4,000 gallon tender with scoop, vacuum brake for train. Eventually fitted with shorter chimneys, scoop removed
||Engines cut down to suit NBR load gauge. All transferred to O4/1 in December 1946. Prior to 1925, O4/2 referred to 3 engines with 3,250 gallon tenders.
||Ex R.O.D. engines purchased by LNER. Similar to O4/1 but without tender scoop and with steam brake only (Westinghouse too when R.O.D.). Merged with O4/1 in December 1940.
||Rebuilds with O2 type boilers (5' 6" diameter and round top firebox). Frames lengthened at rear end, new cab with single side window, GN type chimney.
||Rebuilds with shortened barrel version of O2 boiler. Original cab retained. GN type chimney.
||Conversions from class O5 with standard O4 boiler (from 1922 onwards). Wide cab (some with double side windows) retained.
||O2 type boiler with shortened barrel and firebox. Original cab retained. GC type chimney.
||B1 type boiler (5' 6" diameter and round top firebox). New cab with double side windows. GN type chimney.