Convert,compare all Imperial tool,nut,bolt and spanner sizes to metric. (original) (raw)

Kevin C Bacon.(Baconsdozen Imperial tools).

**Commonly used Whitworth or B.S.F to SAE / A.F (inches across flats) sizes and conversions to metric and decimal inch dimensions.

Spanner and socket sizes/comparisons of metric,imperial.BSW,BSF and BA sizes.

I've prepared these charts from my own experience and research.They are all my own,original work,not plagarised from other web sites or the 'experts' on ebay.If they appear anywhere else,they have been copied from here.

Commonly used Whitworth/BSF thread diameters and the mm or imperial (inch) size of the wrench opening (across flats) to fit nut or head.

Notes.
*You can use the above chart (and the AF/metric chart below) to find equivalents for some missing tools.For example 5/8 inch whit and 28mm,3/4 inch whit and 33mm etc. Some sockets especially six sided impact might be marked in these examples with both sizes.

The much longer list at the bottom of the page lists all common wrench or spanner sizes in size order,and is intended to assist finding alternative sockets etc for damaged fixings .

** 11/16 inch is not a commonly encountered Whitworth size,13/16 inch and 15/16 inch are even less so and were very seldom specified on engineering drawings etc.

Before about 1948 BSW and BSF nuts and bolts (needing BSW/BSF tools) were commonly used on cars,motorcycles and machines especially those made in the U.K. After this date they were gradually phased out and replaced by UNC (Unified Coarse) and UNF (Unified Fine) both needing Imperial AF tools.There are two 'standards' of Whitworth/BSF sizes (see foot of page) but the same spanners can be used on either .Some older motorcycles use B.S.C (British Standard Cycle) threads and spanners marked BSW or BSF will fit these.By about 1965 BSW and BSF were considered obsolete although they may still be found in later,specialised applications. By the end of the 1970s UNF and UNC had almost gone the same way,replaced by the metric although they too can still be encountered in post 1970's machinery.Consulting an owners club,workshop manual etc and using the info on this page will help select the spanners you need but previous owners may have fitted other fixings and parts and many makers would use an assortment of fixings even during manufacture.Try to avoid damaging your nuts with the wrong spanners.

A few explanations.....

British Standard Whitworth (B.S.W) takes its name from the British engineer who invented it as a way of standardising bolt and nut sizes.This was in the days when Great Britain had a large manufacturing base and didnt simply import cheap junk from the far east.Whitworth threads are based on an angle of 55 degrees. Commonly found on older (pre 60's) vintage,veteran and classic cars,bikes or early machinery,there are two 'standards' of Whitworth, as the sizes of nuts and bolt heads were reduced to save stocks of iron and steel.They were all reduced by one size,so that the same spanners and sockets can still be used. The war also demonstrated the need for a standard for nuts.bolts and the tools to work on them as British (mainly BSW and BSF) and US (UNF and UNC) machinery used completely different systems.

British Standard fine is in effect the fine version of whitworth with the same thread form but with a greater number of threads per inch.The size marked on a Whitworth or B.S.F (British Standard Fine) spanner refers to the diameter in inches of the threaded portion on the bolt it fits. Both Whitworth and British Standard Fine were phased out by the 1960s,but some manufacturers carried on using both on applications much later than this. Whitworth thread is coarser than a BSF of the same diameter,but the same spanners are used on both ranges,and are often marked with both Whitworth and BSF sizes .A whitworth spanner or socket is larger than one marked with the same size in BSF for example a 1/4 inch whit is the same physical size as a 5/16inch BSF.(approx 13.34mm),this occurs throught the sizes so a set of whitworth sockets or spanners will fit an equal number of BSF nuts and bolts.The easiest way to identify a whitworth or BSF threaded bolt is to measure its diameter and check the thread rate (TPI or threads per inch) with a thread gauge and compare it to the charts below.BSW and BSF socket head screws use AF hex keys not metric.

B.A (British Association) are smaller sized fastenings found on older vehicles electrical fittings,magnetos,dynamos,motors,pumps and instruments etc. B.A thread has an angle of 47 degrees-30 minutes.This was another standard introdued to try and rationalise the sizes of smaller fixings,and which now confuses greatly the metric spanner wielding enthusiast.

A.F means Across Flats and indicates the distance apart the jaws are on an open end wrench (or the parallel sides on a nut or bolt. Usually applied to spanners in imerial (inch based) sizes the smallest increments are normally 1/16 inch (for example 7/16,1/2,9/16 etc) but some smaller spanners are marked in 1/32 inch increments.Very rarely af spanners are marked in decimal instead of fractional sizes for example .50 instead of 1/2 or .75 instead of 3/4 inch etc.Imperial AF spanners are normally used on nuts and bolts threaded UNC or UNF (Unified Coarse or Unified Fine) and use a thread angle of 60 degrees.This standard was introduced as the 'new' standard around the 1940s to replace BSW and BSF etc and was supposedly phased out by the 1970's in favour of metric threads and sizes. However like Whitworth and BSF, AF it is still encountered in specialised applications and many car and motorbike makers carried on using imperial fittings etc for a long time after they became supposedly obsolete. It is very common to find an older car or bike that left its maker with a mixture of imperial and metric nuts and bolts holding it together. Land Rover and other smaller,specialised car makers used a mixture of imperial fittings into the 1990's.Note also that AF allen or hex keys fit BSW or BSF hex headed socket screws.
Modern metric spanners are marked or sized in the same way as AF but in millimetres,the distance again between parallel faces of an open ended spanner or wrench.They are used on metric threaded fastenings,these have a thread angle of 60 degrees.Metric bolts often have two numbers on the heads,this is a strength rating.

Coarse threads (whitworth,unc etc) are more likely to be used on the thread in a casting (especially aluminium) to give greater strength,most nut and bolt assemblies will use a fine thread,so studs in castings often have a coarse thread end to go in the casting and a fine end to take a nut. Finer threads (BSF,unf etc) have a greater resistance to being shaken loose by vibration.Bolts and nuts in brass or similar soft metal are normally coarse threaded for greater holding power..

AF spanners and sockets (across flats in inches) to Metric (mm).

Diameter and thread pitches in inches (tpi) for BSW, BSF, UNC and UNF bolt threads
This chart can be used to help identify the thread on a bolt etc. Measure the outside diameter and then count the number of threads per inch. UNC and Whitworth have the same thread rates but the thread form is different,a thread gauge would help to make accurate comparisons.Take into account also the age of the vehicle or machine the fitting is from. Pre 60s Whitworth is more likely,unified threads started replacing BSW and BSF from the early 1950s but the change was spread over many years in some cases.

BA spanner and socket sizes in inches with metric (mm) equivalents

BA (British Associated) is an early British standard often found on dynamos,magnetos,distributors,starters and electrical fittings and connections on older British cars and motorcycles.

The smaller the number the larger the BA nut and bolt. BA sizes right down to 24BA are in fact used.although 10BA is the smallest normally encountered.The thread per inch rate is always a fraction (ie) never a whole number varying from 25.4 (0BA) to 72.6 (10BA) for example.The logic for this is buried in the mists of time.

As a rough guide the diameter of a 0BA bolt is approx mm,2BA is 4.7mm,4 BA is 3.62 and 6BA 2.80mm.

Application chart for some hub nut,ball joint sockets and box spanners etc (mainly older vehicles).

All the commonly used spanner and socket sizes,from 10BA up to 60mm with their decimal inch equivalents.

This chart shows comparative sizes in increasing B.A, A.F, B.S.W, B.S.F and MM bolt or nuts and can be used for example to find the next size up or down where a spanner (wrench in USA) or socket is too tight or loose on a fixing. It also shows when some spanners and sockets are almost the same physical size although displaying different markings for example 11/32 inch AF and 1/8 inch whitworth are identical. Note that a set of spanners marked in whitworth (often abbreviated just to 'W') or sockets will cover both the whitworth standards (pre and post war) and the BSF ranges, you do not (as some naughty or just ill informed web sites suggest) need to buy two sets!.

0.117 inches =10 BA

0.131 inches = 9 BA

0.152 inches = 8 BA

0.172 inches = 7 BA

0.193 inches = 6 BA

0.220 inches = 5 BA

0.248 inches = 4 BA

0.250 inches = 1/4 inch AF

0.276 inches = 7mm

0.282 inches = 3 BA

0.313 inches = 5/16 inch AF

0.315 inches = 8mm

0.324 inches = 2 BA

0.344 inches = 11/32 AF and 1/8 Whitworth

0.354 inches = 9mm

0.365 inches = 1 BA

0.375 inches = 3/8 inch AF

0.394 inches = 10mm

.0406 inches =13/32 AF (10.3mm)

0.413 inches = 0 BA (Largest BA size)

0.433 inches - 11mm

0.438 inches = 7/16 inch AF

0.445 inches = 3/16 Whitworth or 1/4 BSF

0.472 inches = 12mm

0.500 inches = 1/2 inch AF

0.512 inches = 13mm

0.525 inches = 1/4 inch Whitworth or 5/16 BSF

0.531 inches = 17/32 inch AF (13.49 mm)

0.551 inches = 14mm

0.563 inches = 9/16 inch AF

0.591 inches = 15mm

0.594 inches =19/32 inch AF (15.1 mm)

0.600 inches = 5/16 Whitworth or 3/8 BSF

0.625 inches = 5/8 inch AF

0.630 inches = 16mm

0.669 inches = 17mm

0.686 inches = 11/16 inch AF

0.709 inches = 18mm (uncommonly used metric spanner size) but often used as a substitute for 3/8 inch whit..

0.710 inches = 3/8 Whitworth or 7/16 BSF

0.748 inches = 19mm

0.750 inches = 3/4 AF

0.781 inches =25/32 inch AF (19.8mm)

0.813 inches = 13/16 AF inch (Common spark plug size).

0.820 inches = 7/16 Whitworth or 1/2 BSF

0.866 inches = 22mm

0.875 inches = 7/8 inch AF

0.920 inches = 1/2 Whitworth or 9/16 BSF

0.938 inches = 15/16 inch AF

0.945 inches = 24mm

1.000 inch = 1 inch AF

1.010 inches = 9/16 Whitworth or 5/8 BSF

1.024 inches = 26mm

1.063 inches = 1 + 1/16 AF inch or 27mm

1.100 inches = 5/8 inch whitworth or 11/16 BSF

1.105 inches = 28mm often used as a substitute for 5/8 inch whit (actually .005inch larger).

1.125 inches = 1 + 1/8 inch AF

1.181 inches = 30mm

1.200 inches = 11/16 Whitworth or 3/4 BSF

1.250 inches = 1 + 1/4 inch AF

1.260 inches = 32mm

1.300 inches = 3/4 Whitworth or 7/8 BSF

1.313 inches = 1 + 5/16 inch AF (some ball joints).

1.390 inches = 13/16 Whitworth or 15/16 BSF (not very commonly used).

1.417 inches = 36mm

1.438 inches = 1 + 7/16 inch AF

1.480 inches = 7/8 Whitworth or 1 inch BSF

1.495 inches = 38mm.

1.500 inches = 1 + 1/2 inch AF

1.575 inches = 40mm or 15/16 inch Whitworth

1.614 inches = 41mm

1.625 inches = 1 + 5/8 inch AF

1.670 inches = 1 inch Whitworth or 1 + 1/8 BSF

1.688 inches = 1 + 11/16 inch AF

1.811 inches = 46mm

1.813 inches = 1 + 13/16 inch AF

1.860 inches = 1 + 1/8 Whitworth or 1 + 1/4 BSF

1.875 inches = 1 + 7/8 inch AF

1.969 inches = 50mm

2.000 inches = 2 inch AF,(A fairly common hub nut size).** see notes in above table.

2.047 inches = 52mm (Some land rover hub nuts) used as substitute for 1 + 1/4 inch whitworth (actually .003 smaller).

2.050 inches = 1 + 1/4 Whitworth or 1 + 3/8 BSF,(another common hub nut size).

2.065 inches = 2 + 1/16 inch AF

2.165 inches = 55mm

2.362 inches = 60mm

A tubular box spanner or six sided socket the next size up might be a solution when the correct size is not available (ie) a 19mm spanner will probably undo a 3/4 inch af nut.These may have greater tolerance than 12 sided sockets but there is always a risk of damage to socket and or the fastening. Most impact sockets are six sided. Six sided (sometimes called six point) sockets or ring spanners are also less likely to damage brass or chrome plated fittings.

Whitworth,BSF,metric and imperial spanners are based on different standards and hence sizes,with few exceptions they are not interchangeable..As well as classic motorcycles from AJS to Vincents,a lot of older cars used whitworth and BSF fastenings .Marine engines like Lister and Gardner use them as well, and were designed to last, so imperial tools might be regarded as obsolete by some but are still essential on such units..
Damaged bolt heads spoil the restoration or repair of many a rebuilt classic car or motorcycle,theres no need when the correct spanners are still available .Ring spanners are called box spanners in the U.S. .A block spanner is another term for an obstruction spanner and some people refer to C obstruction spanners as crescent wrenches,others use the same term for an adjustable spanner.

If you are still unsure as to what spanner or socket you require to order,measure the nut or bolt with a caliper or accurate ruler across the flats in mm.If you know if the thread is fine or coarse and when the item was made it will help work out what size the original fitting is. Some axle shaft nuts are eight sided,normal bi hex sockets will not fit these

My Home page is here.

Some web sites state that Whitworth and UNC fixings are interchangeable.This is not strictly correct,although some will loosely 'fit' the thread angle on Unified threads is 60 degrees against the 55 of Whitworth.The thread rates are also different (ie) 1/2 inch whit is 12 tpi and for 1/2 inch UNC is 13.tpi. Other thread forms that may be encountered on older machinery include BSP (British Standard Pipe) on fuel,air or oil lines etc and very rarely and on much older machinery BCS (British Standard Cycle).

Kevin C Bacon

Baconsdozen Imperial tools

Tel (44) 01472353993 (answer phone is on to avoid scammers) Mobile 07974435627..