The Nuts and Bolts of Vintage British Motorcycle Hardware

To many British motorcycle enthusiasts, few things rival the anticipation and thrill of opening a recently delivered box of parts from their supplier. The glistening chrome rims, exhaust pipes, and petrol tank emblems are a sight to behold, and the brand-new electronic ignition kit and wiring harness just add to the excitement when the contents of the box are surveyed. What are the last items to be accounted for? Why, of course it’s the little sealed bags with spring washers, lock nuts, bolts, and other hardware bits. Given the array of thread forms on vintage British motorcycle hardware, it merits a short explanation of what to watch for when replacing hardware.

Of course, a factory parts catalog is an absolutely essential guide for ordering hardware, or any part for that matter when undertaking a refurbishment of a vintage BSA, Norton, or Triumph motorcycle. There were a number of common thread types used over the years until the late-1970s, when it was almost completely standardized to Unified threads on nuts, bolts, and studs. Let’s take a brief look at the fasteners used on post-war machines:

British Standard Whitworth (BSW)

BSW is a coarse thread with a 55 degree included angle. Often found on fasteners that are threaded into an aluminum casting, such as early cylinder base studs. By the late 1950s, Whitworth threads were largely phased out of use on the common British motorcycles.

Cycle Engineers Institute (CEI)

CEI is a fine thread with a 60 degree included angle. This thread form was used on the majority of fasteners on British motorcycles until the late 1960s. Also referred to as British Standard Cycle (BSC), or simply “cycle thread”, these nuts and bolts require Whitworth spanners and sockets for fastening and loosening and are often mistakenly referred to as Whitworth.

British Standard Fine (BSF)

BSF is also a fine thread, similar to CEI, but with a 55 degree included angle. BSF screws were often used as case cover screws in machines from the 1950s and 1960s.

British Association (BA)

BA threads are used for screws, bolts, and nuts ¼” and less in diameter, as found on electrical switches and other light-duty applications.

Unified National Coarse (UNC) and Unified National Fine (UNF)

UNC and UNF are threads with a 60 degree included angle and are known as SAE or American threads. These fasteners started making their way onto British motorcycles starting with the 1967 model year, and transitioning all the way until the mid-1970s, when the majority of fasteners were UNC and UNF.

Here at The Bonneville Shop, we are committed to providing the necessary hardware to complete the refurbishment of your Triumph motorcycle. We offer a number of kits containing the necessary hardware for engine-to-frame installation, as well as cylinder head bolts, case cover screw sets, and many more.

Most recently, we have updated many of our hardware-related products by including variable quantities available for a given part number. For example, the 14-1304 7/16 x 20 TPI Cleveloc nut is now available in multiple quantities of Single, Four, or Ten, with significant pricing advantages when purchased in quantity. By emphasizing hardware, we are committed to the details of safety and the preservation of vintage British motorcycles.

As a hardware geek, I’m dedicated to making those bags of hardware the first thing to inspect when opening the box of parts from your supplier.

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