The Westinghouse Brake & Saxby Signal Co. Ltd produced the Style 'B' mechanically locked lever frame from 1902, The styel 'B' lever frame was developed from the style 'A' lever frame of 1902. The first style 'B' was installed at Harton Colliery [South Shields 4½ miles [8 km] NNW of Sunderland ] in Dec 1902.

The follow on Style 'K' lever frame was introduced in 1912, and there is not much difference between the two, the 'B' lever frames were only used abroad until 1923. The 'K' lever frame of course was designated to be the "all-electric" version whereas the B had first been designed for electro-pneumatic use at sites which Southport Chapel Street was.

As far as the differences between B and K go there aren't really any other than the K usually had a greater number of contact bands because these were normally used for all-electric installations whereas the B was first designed for electro-pneumatic operation. Both had teak casing but LT companies often went for steel, similar to the L and N styles. I guess there were probably subtle changes to materials and parts between the B and K as there was a time separation between the first Bs and the introduction of the K so opportunity would have been taken to make improvements or economies. So the answer is that I've not come across any significant difference, it's more a case of marketing a "new" version by Westinghouse at the time because it's also not unknown for Ks to be used on electro-pneumatic jobs. Hope this helps Regards Mark

The table below in green shows the locations of the frames supplied and installed by Westinghouse Brake & Saxby Signal Co. Ltd