The Great Western Railway became dissatisfield with their double twist and stud locking frames and in 1904 developed their own tappet interlocking. Within 5 years they had designed three different versions!

This paper explains the principles on which these interlockings are built and, with the use of many diagrams, how they operated.

In this paper you will also find an explanation of locking tables and dog charts and how they relate to some sample layouts.

Written by one of our members, Reg Instone, this paper is key to understanding how mechanical locking operates and the principles explained are equally valid for other railway company's tappet locking. Modellers who wish to replicate prototype signalling and use it correctly on their layouts also need an understanding of interlocking and this is an excellent primer in the subject.

This signalling paper is supplied as a downloaded PDF format file and can be read by pretty well any computer, tablet or mobile phone.

If you pay us by PayPal you will be able to download your file immediately. If you pay by other means then we will email the file to you, usually within a couple of days of our receiving payment.

We also do a version of this paper in which many of the diagrams are animated. Follow this link to discover more.

Need this on a different media? Contact us via the link at the bottom of the page and we'll see what we can do.