Types of chairs used over the years were either for fish belly, "T" section, double head or bullhead rails.
"T" section rail and its chairs could be found into the nineteen eighties in rarely used and long un-relaid sidings.
Double-head chairs differed from bullhead chairs because the foot of double head rail was larger than the foot of bullhead rail. Thus it was possible to put bullhead rail into double-head chairs but not vice versa.
A very common design of double-head chair was the 'S' chairs which had only two spike holes and which when looked down on from above looked rather like a letter 'S'. These chairs had very high cheeks on the inside of the chair's jaw and with worn double head rail the wheel flanges were coming into contact with the chairs - a very unsatisfactory state of affairs. Other more modern designs of double-head chairs had oblong bases and lower cheeks on the inside jaw. The design had no doubt evolved to remove the problem of flanges striking chairs. The number of spike holes varied from two to four. One pattern had two holes set far apart - ideal for straddling cracks in timber sleepers. By the mid-nineteen sixties when double-head track was re-sleepered only oblong based chairs were used and the 'S' pattern chairs were being eliminated on the main line. Use of track screws required the spike holes to be drilled out to make them slightly larger. This was originally done at Boston Lodge and then the old drill used for this purpose was moved to Minffordd goods shed. Drilling chairs was one of many "wet day jobs".
Bullhead chairs all had oblong bases with 2 to 4 spike holes. Penrhyn Quarry Rail chairs came in two styles, two hole or four hole. There were many slightly different designs of FR bullhead chairs.
For both double-head and bullhead chairs there were many specialised designs for particular purposes. For example check rails required special chairs that accommodated the running rail and the check rail. As well as on curves, these were required for check rails on turnouts and level crossings. There were also different designs of slide chair to hold the stock rail and accommodate the switches of turnouts - different for every type and weight of rail. In addition there were specially cast chairs to give superelevation (or cant) on curves such as at Tan y Bwlch road under bridge. According to Boyd, "on sharp curves a special chair with thickened base was used to carry the outer rail." (Boyd 1975) For a discussion of the use of these chairs see Tyler's Curve. In his report on an derailment at Coed-y-Bleiddiau in October 1901 Major E Drewitt suggested excessive cant of 3 inches for the speed of the train led to the spreading of the inside rail. (see Day Log/1901-10-04.)
Boyd J I C, 1975 The FR, page 378.
Flat Bottom & Bridge Rail
These types of rail rest flat on wooden sleepers and do not need chairs. Sometimes base-plates are used which may be designed for particular types of rail fastenings such as Pandrol Clips. Base-plates hold and locate flat bottomed rail but cannot be used with double-head or bullhead rail.