Every so often, we come across a request to match a fastener that doesn’t immediately fit any of our sizing templates for ANSI or ASME threads. When this happens, we start by asking for the application or origin of the fastener we’re trying to match, and if the answer comes back indicating an origin in the UK, we can be reasonably sure that we’re dealing with British Fasteners, using a British Standard Thread. Though rare in North America and largely being replaced by more common global standard fasteners, British threads have a wide range of options in use today, as well as an interesting history, all of which we’ll review in this article.
British Thread Types
Getting familiar with British thread styles allows for an interesting diversion into English history, centered on English entrepreneur, engineer, and inventor Sir Joseph Whitworth. Across his 19th century career, Whitworth aspired to produce increasingly precise machinery, inspired in part by keeping company with a host of contemporary inventors and machine builders across London, Manchester, and Liverpool. Whitworth has many credits to his name: serving as President of the Institution of Mechanical Engineers, founding multiple technical education centers, serving as British Commissioner for the New York International Exhibition, and in 1869, posthumously being appointed a royal Baronet by Queen Victoria.
In 1841, Whitworth produced a standard screw thread design based around a thread angle of 55 degrees that would soon become the first nationally standardized screw thread system in the world. It’s upon this 55 degree thread angle standard that most of today’s British threads are founded.
Here we’ll take a look at the most common British fastener thread styles that we might come across in North America:
| British Thread Style Name | Description |
| BSW | British Standard Whitworth 55 degree thread angle. World’s first standardized thread form, created in 1841. These threads are measured in Imperial units, governed by British Standard BS-84:2007. Found today in military, maritime, railroad, and certain industrial applications. |
| BSF | British Standard Fine Based on BSW, also 55 degree thread angle. Found today in fine machinery and tooling, and steel bolting applications. Historically common in motorcar, motorcycle, and vehicle applications as well, 1908 and forward |
| BSC | British Standard Cycle Similar to BSW but with 60 degree thread angle. Today found on bicycle components manufactured to British specs (under modern nomenclature as the CEI Thread / Cycle Engineering Institute). Historically found in motorcycle and bicycle components, designed to withstand high torque and vibration. |
| BA | British Association screw thread Similar to BSW but with 47.5 degree thread angle and in metric units. Found today in miniature instruments and modeling such as clocks and watches, small sizes (6mm and smaller), and in some electrical components (conduit boxes, receptacles, switches). Governed by British Standard BS-93:2008. |
Outside of the fastener world, the Whitworth thread form is also found in British pipe threads (BSP), British Standard Conduit threads (BSCon), Model Engineers threads for small modelling applications (ME), and British Standard Copper applications (BSCopper).
Specifying and Ordering British Fasteners
Obtaining British fasteners today is just as straight forward as with more common ANSI and ASTM varieties. Generally speaking, you’ll need fastener style, diameter, length, thread specification, material, and finish information available, just as you would for other fasteners. We’ll walk through each of these items below.
Fastener Style –
Here you’ll specify the fastener that you’re after. We’d recommend using the usual North American terminology when buying through a domestic distributor, letting them make the translation to foreign terms where there may be some minor differences. For example, a ‘fillister head screw’ in ANSI standard terms might be more commonly known as a ‘raised cheese headset screw’ in British standard terms.
Diameter and Length –
Same as with any other fastener, you’ll specify the common diameter, overall length, and thread length (if not fully threaded). Here you’ll specify units as well (mm or inches).
Thread Specification –
Here we have a variety of British specifications to review. For brevity, we’ll list the common specs below that you may choose to research and confirm meet your application, or you may discuss in more detail with your distributor. When speaking with your supplier, it may be easiest to mention the application that the fastener will be placed into, helping them to narrow down the specification options that way.
- BS57 Nuts
- BS93 BA Socket Head Screws
- BS1083 Imperial Hex Head Screw
- BS3392 Metric Hex Head Screws
- BS2470 Socket Head Screws
- BS4320 Flat Washers
- BS4463 Crinkle Washers
- BS4464 Spring Washers
Material –
Most British fasteners are available in the same materials that we are familiar within North America. For the sake of finding stock and lower prices, the most common materials available domestically are Steel, Hardened Steel Alloy, Stainless Steel, and Brass.
Finish –
Also for the sake of finding stock and lower prices, bare or plain finishes may be your best bet. Second to that, common finishes include silver zinc plated, yellow zinc plated, and black oxide.
Additional options are certainly available, possibly impacted by order volume, lead time, and price considerations. Post-treatment, heat treatment, special hardening, exotic materials, and unique finishes are all options for British fasteners.
E&T Fasteners is here to help you navigate fastener options to best meet your application and project needs. Price quotes, availability, lead times, delivery confirmations, unique application suggestions – whatever your need, we’re here to take your call or email. For support and advice from our fully trained staff, speak with an E&T sales representative today.
About E&T Fasteners
With sales and support teams spanning the Continental US, E&T Fasteners is here to serve your hardware, fastening, and component needs both domestically and internationally. We are a stocking distributor of metallic, plastic, and exotic alloy fasteners, backed by our technical staff directly experienced in your unique applications. We can assist your specifying and selection efforts, providing engineered solutions, record-fast lead times, and stellar customer service from quote through delivery. Please let us know how we can help!
