Hilary many thanks for your help and input. I agree with what you say all post war Maclean frames start with the letter "K" prefix. They restarted production in 1946. They never put their builders back onto piece-rate until 1948. I better expand on this as to what the two ex Macleans builders told me. 1946 restart of building first frame K 1. no piece rate in workshop due to shortages of frame tubes. 1948 return to piece-rate because tubing steel restrictions relaxed so frame number K plus builder mark letter. If this was a sequential numbering and lettering system why would you find KA used in 48 and 49, KB in 50, KC 55 and KD in 58, 59. 60 ? These are big gaps and they were prolific builders. No I am sure what Tom Board says is correct the second letter is the builders identification. The other builder was Jumbo Wilkinson a great mate of Hyman Samuels (Sammy) ex Hetchins and both CTC and Southgate. Fascinating. Croeso Cymru Joe King Nr. Maenaddwyn Ynys Mon Wales