When you see a spanner marked AF, it stands for Across Flats but is actually an Imperial size inscription or more specifically an SAE marking which is associated with UNF and UNC screw threads. For instance, a 1/2 inch AF spanner means it is a ½ inch across and can fit in a 5/17 inch UNF nut’s diameter.

Everything You Need To Know About Spanner Sets | RS

Spanner set uses are many and varied, but all jobs for which a spanner is required will generally involve loosening or tightening nuts and bolts of some description. The precise function and application of a particular spanner set will depend on the job in hand, which in turn is dictated by the type and size of spanner required for a given bolt or nut. The Whitworth system dates from 1841, and was the first non-proprietary bolt size system to be widely adopted. It describes bolt head sizes and bolt threads. There are 4 whitworth bolt designations, known as: Sizes are only listed under the 'fits' column where the imperial size is in general use (or was). 29/32" may be a good metric fit, but no-one has such size tools.It is used in situations whereby an inaccessible position needs to be reached to tighten bolts and nuts which have very tight threads that can’t be undone using fingers.

Socket Set: Choosing spanners for DIY | Hagerty UK Socket Set: Choosing spanners for DIY | Hagerty UK

They are wrenches with a single or many hooks and pins designed for the purpose of driving retainer rings and collars and other related screwables.An imperial spanner set, rather than denoting a particular function or a specific type of head or shaft design, is simply a spanner set of any kind that has been constructed for fasteners defined by imperial measurements (inches and fractions of inches, rather than millimetres). British Standard Whitworth ( BSW) is an imperial-unit-based screw thread standard, devised and specified by Joseph Whitworth in 1841 and later adopted as a British Standard. It was the world's first national screw thread standard, and is the basis for many other standards, such as BSF, BSP, BSCon, and BSCopper. Metric spanners are fairly straightforward to understand in that the size given on the spanner, say 13mm, refers to the distance in millimetres across the flat-sided surfaces of a nut or bolt head. The same is true of Imperial “AF”, found on American classics and UK cars built after 1960. AF is short for “across the flats” and again, it’s a literal measurement so if the spanner is marked 1/2 then it means the distance across the flats of the nut or bolt it fits is 1/2 an inch. This is the most expensive set on test, but you do get a lot for your money, not just in terms of the number of tools, but also their size. All our essentials are present, but if you work on larger vehicles, there are also common sizes up to 32mm. So as you can see above, once you know you have a metric M10 nut, then you can easily read off the chart then you need a spanner stamped with 17 mm. No need to guess