The Westinghouse Brake & Saxby Signal Co. Ltd produced the Style 'N' mechanically locked lever frame from 1931, and a total of 40 units were shipped for use on London Transport underground railways.

The 'N' style frame was a mechanically locked version of the Style 'L' power lever miniature lever frame, it had the mechanical locking situated at the front under the lever instead of the electrical circuit contacts. As a result the electrical circuit contacts {bands} were always placed at the read of the lever frame. From a user point of view the lever frame looked and felt the same as the Style 'L' lever frame. 

The first table in Green, shows all the locations of all frames supplied and installed by Westinghouse Brake and Signal Co. The second table on Yellow lists the preserved Style N lever Frames.

Points show the normal and reverse indications and if the extrusion plate for the point has a red label then the points are fitted with point heaters.

There are no block bells in any LUL box the previous exceptions were Harrow on the Hill and Amersham because they worked absolute block to a BR box (Neasden South in the case of Harrow and Great Missenden, Wendover or Aylesbury in the case of Amersham) but these ceased to have block working with the coming of Marylebone IECC.

The train describer receivers were part of the diagram (rather than mounted on the shelf) usually mounted in wings on each end but some times in the main diagram as in the case of the White City photo on the site.

All the LUL N frames had a slightly different lever (as you probably already know) from the L frame in that in front of the catch handle is a protrusion where a small metal plate is fitted with the lever number on. The N frames also had device called "Ball Catch Break" which will cause the lever to disconnect itself from the lever locks and band shaft if the lever is forced against the locking. I have absolutely no idea what this looks like and would love to see it 'cause it seems like a good idea to me.

All LUL frames were larger than the total number of levers by about 2 or 3 feet to accommodate a desk for booking as most (if not all) LUL boxes record train passing times and all LUL boxes have metal cases to the frames because Mr Dell said so (fire precautions).

All LUL diagrams except those in the control rooms show track circuits clear as lit, the opersite of most mainline boxes although both Neasden South (ex GCR) and Earlswood (ex LBSCR) were the same as LUL when I first saw them (in fact Neasden South was until it closed).

I have to say I visited a number of LUL boxes most of them on the spare of the moment and therefore have no pictures, I especially regret not having any pictures of White City as I visited there one Christmas Eve and had a play. I also visited Hammersmith (Met) but never photographed that. Two which I serverely regret are West Ruislip and Finchley Road because these had large N frames with route setting.

I also visited Baker Street (Bakerloo) hidden in a tunnel just off the public area, this frame was a K with just 9 levers but the poor guy working it had to call the station Supervisor to relieve him if he needed the toilet! But my favourite LUL box is Edgware Road which is both the only K frame still in full time regular use now and also one of the few interesting LUL boxes service wise.

I'm sure you know most of the above but I thought as my head was running I'd write it all down as it came. Somewhere I have a picture of West Kensington East IMR which had an N2 frame and if I find it I shall pass it on to you. With thanks to Graham Floyd