The Stanier boilers came in 3 series which were all taper. The 1 series were for the pacifics but there are big differences between the Princess series and the Coronations. For a start those on the Coronations were shorter. The boiler made for 6202 was never fitted and became the spare for the first 2. 6202 was fitted with the one originally intended for 6203. When within a very short space of time, 6202's boiler was changed, the original went into the pool of spares for the second series but had the difference that it had 32 superheater elements. The replacement was not only domed but it had a 40 superheater. None of the other Lizzie's had 40 elements. The boiler for 6200 and 6201 were always slightly different and were not interchangeable with the rest of the class. So although all the pacifics were fitted with No 1 boilers, there were quite marked differences between locos. It was further complicated as the original boilers were not good steamers and some of the later series had combustion chambers. As a matter of interest, the 2 series were intially to British Legion and the a slightly shorter modified version fitted to the 7P rebuilds. The 3 series were fitted to the Jubilee's, Black 5's and 8F but again with variationd and not just with or without domes. Initially they had a vertical throatplate and long boiler. This was soon changed to a slightly shorter boiler with a sloping throatplate. Even within a single class, the 2 types were not interchangeable as the frames were different. Some of the early vertical throat plate engines had their frames changed and were fitted with the sloping ones. Their old boilers then went to form a pool of spares for the earlier engines.