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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 four Tyer'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 measure 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
==Method of Operation==
If signalman A wishes to send a train will send the "Call Attention" bell signal. When signalman B at the other end of the section acknowledges the "Call Attention" bell signal signalman A will send "Is the line clear for (the particular type of train)" n.b. there are different signals for different train types. If the signalman B accepts the train they will respond by repeating the bell code but keep the bell plunger held in on the final beat of the signal. Keeping the plunger held in releases the mechanism of signalman A's token instrument if no other token has been removed, so he or she can remove a token. When signalman A withdraws the token from the instrument both signalmen will set their indicators to show that a token is out, and which direction it is travelling in.
Removing the token will unlock the section signal which allows trains to enter the single line between the two signal-boxes. Signalman A will clear this signal, put the token into a token carrier, and give it to the footplate crew. The token recipient will read out loud the signal box names as a further means of checking they have the correct token for the single line section they are to pass over. As the train departs, signalman A will check it is showing the correct tail lamp at the end of the train, and send "Train Entering Section" to signalman B.
When the train arrives at the far end of the section the crew will hand the token, in its carrier, to signalman B. When signalman B has seen the tail lamp on the back of the train or the guard has confirmed the train has arrived complete signalman B will place the token in their instrument, put their indicator to normal, and send "Train Out Of Section" to the signalman A.
Signalman A will then return the indicator to normal. Both signalmen will record each of the above events along with the time they occur in the Train Register.
