General Hardware & Fixings
Following is a listing of common fasteners. These fasteners are for general use and are not intended to replace those listed for specific applications elsewhere in this catalogue. TR’s were fitted almost exclusively with UNF/UNC hardware.
UNF/UNC were threaded forms introduced into the USA during the 1940s (World War II) to give stability and standardization to various industries (automotive in particular). It became standard in the British car industry in the 1950s. UNF stands for "Unified National Fine" and UNC "Unified National Coarse".
To aid identification by terminology, a screw is threaded for its full length. A bolt is only part threaded with a plain unthreaded shank area between the head and the thread. The part number two letter prefix of SH means that the item is a Screw with a Hexagon head. The prefix BH means a Bolt with a Hexagon head. The first number defines the thread type, UNF = 6, UNC = 5. The second and third numbers give the thread diameter in increments of 1/16", e.g. 04 = 1/4", 05 = 5/16", 10 = 5/8". The fourth and fifth digits show the length in increments of 1/8", e.g. 04 = 1/2", 16 = 2", 23 = 2 7/8". The last digit defines finish, 1 = zinc plated. This coding system is only applicable to bolts and screws; nuts and washers are coded by a similar system that follows some of the above principles.