Extract from Handbook For Permanent Way Staff (1958).

The various rails in use are distinguished by their weight expressed in pounds per yard and by the section to which they are rolled. The rail section which finds almost universal acceptance today is the "T" section or flat-bottomed rail. It is designed as a girder to distribute a wheel load over several adjacent sleepers and is the development resulting from earlier failures and weaknesses.

Prior to 1905 no uniformity of rail section had been adopted by the Department and rails were rolled or purchased as seemed convenient and suitable to meet its requirements. These were produced in 40 lb., 53 lb., 56 Ib., and 70 lb. to the yard. Sometimes, these rails, though produced in England, were rolled to American rail sections. In 1905 the first British Standard rail designs were published, and at that date the Department adopted the British Standard sections and these remained in use until about 1930. The weights used during this period were 55 Ib., 70 Ib., and 100 Ib. These rails are known to the track staff as "Old British Standard" or simply as "O.B.S." rails.

In 1924 the 1905 standard rail sections were redesigned generally increasing the height whilst leaving the width of base unaltered. The weights of these sections used by the Department were 70 lb., 75lb., 85 lb., and 100 Ib. It is now the practice by track staff to designate the rails rolled to the 1924 standard as "New British Standard" or "N.B.S.". Officially, they are known as "Revised British Standard" or "R.B.S." rails, and are distinguished by the letter "R " following the weight on the rail brand, thus -70 R. No further bulk supplies of these rails will be purchased.

As a war emergency measure quantity of 75 lb. and 90 lb. rails to standard American designs were imported.

In 1950, following upon the discovery of certain weaknesses in the British Standard sections and the necessity for a slightly heavier rail, the Department prepared its own designs for two new weights and designated these 72 1b, N.Z.R. and 91 1b. N.Z.R.

It may be said, generally, that the length of rails has increased proportionately to the increase in weight with an upper limit of 42 ft. for all standardised rails from 70 lb. to 91 lb. Green ends -shorter rails for use in laying the low legs of curves -are usually in lengths of 41 ft. 81/2 in. for 70 lb., and 41 ft. 71/2 in. for 85 lb., 91 lb., and 100 lb.

OB Open Hearth Bessemer

BS Bessemer Steel

LB pounds (weight) per yard

KG Kg per metre

R (after weight) Revised British Standard (RBS) designed in 1924.

NZR "In house" section designed in 1950

ARA ??

CLD ??

CC ???

GKB PT ??

D L & Co Dorman Long & Co

TRL Toll Rail Ltd or Tranz Rail Ltd.

Details of rail sections can be found at:

http://www.corusrail.com/docs/23e48d703e856dHandbookversion2.pdf

http://www.lbfoster.com/railproducts/Relay_rail_sections.pdf