... entire switch. Indeed there is no need for any different chairs by the simple expedient of skewing the chair on the timber. This is obviously acceptable practice (despite the slight loss of gauge-spread resistance) because it is done for the P slide chairs. That page is for GWR and BR(W ), but given the use of the same designations and the BR revision dates it seems likely that the BR REA designs are similar. But here is a drawing of an REA left-hand A-switch: 2_230740_120000000.png Which shows the P slide chairs skewed, and the block chairs square-on to the timber (with no designations on the chairs that they are for a left-hand switch only). I can only assume this was an error on the original drawing, and that all subsequent drawings have copied the same original. Note also in that drawing the wider S1J joint chairs on the first timber. This photo shows on the right an REA block chair on a right-hand switch. I wouldn't want to swear in ...