Changes

Much like a key for a mortice lock the end of the token that is placed into the instrument is made with four different "wards" to prevent a key being placed into the wrong instrument where multiple instruments are housed in one signal box. E.g [[Highley signal box|Highley]] has an example of all fourTyer's Key Token instruments. Long sections to [[Bridgnorth signal box|Bridgnorth]] and [[Bewdley North signal box|Bewdley North]] plus short sections to [[Hampton Loade signal box|Hampton Loade]] and [[Arley signal box|Arley]].As an additional precaution to deter a signalman trying to insert a token into the wrong instrument the differing tokens are colour coded either Red, Yellow, Blue or Green. This is colour is also carried on the knob on the top of the instrument