Baconsdozen Imperial Tools for older machinery.
To see the Whitworth,BSF and BA tools we sell go here,for AF (SAE) versions go here.
This page is provided to help you select the correct tools for a classic car or bike,older commercial vehicle,boat,plane or stationary engine etc.
 If you buy a pre 70s Britsh car or motorcycle you will soon encounter Whitworth and BSF (British Standard Fine) fixings along with BA (British Association) and possibly BSC (British Standard Cycle) threads. Other than for a very few sizes your metric tools will be of little use and can damage imperial fixings.These Conversion charts will help you understand these different standrads and help you convert Imperial socket,spanner,nut and bolt sizes in  BSW BSF AF BA to metric sizes,and help select the proper tools.
I have no objection to people copying and reproducing parts of this page as long as they credit its authors.Baconsdozen and Kevin Bacon.
Use these charts below to convert spanner sizes in imperial  (BA,Whitworth,BSF or SAE) to millimetres or compare the different imperial spanner and socket sizes to each other . There is also a complete list of all spanner and socket sizes in Imperial and metric standards from 10 BA to 60mm with their equivalent decimal inch sizes. A few of the rarer Imperial sizes are no longer obtainable in some specialised sockets or spanners,use the chart/list at the foot of the page to find the nearest equivalent,probably the easiest way is to measure the fixing across its parallel sides in mm and chose the exact or next size above for a socket or spanner to fit.If in doubt contact us.

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 and UNF (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 BSC (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 during manufacture.

British Standard Whitworth (B.S.W) takes its name from Whitworth,the British engineer who invented it as a way of standardising bolt and nut sizes.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 during world war two the sizes of nuts and bolt heads were reduced to save metal.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 size 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.

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.
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 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..

Whitworth or B.S.F to A.F (inches across flats) and to Metric conversion tables.
Commonly used Whitworth/BSF (pre 1940) head sizes and the mm or imperial (inch) equivalent.
Inches (decimal)
1 .1/8

1 .1/8

1 .1/4



*You can use the above chart to find equivalents for some missing tools.For example 3/4 inch af and 19mm are very close,or 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.

** 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.

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

AF inches


1/4 inch

6.35 mm

5.16 inch

7.94 mm

3/8 inch

9.52 mm

7/16 inch

11.11 mm

1/2 inch

12.7 mm

9/16 inch

14.29 mm

5/8 inch

15.88 mm

11/16 inch 

17.46 mm

3/4 inch

19.05* mm

7/8 inch

22.22 mm

15/16 inch

23.81 mm

1.00 inch

25.40 mm

1.1/16 inches

26.93 mm

1.1/8 inches

28.57 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.

Nominal Bolt diameter inches.














































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.

Number BA

BA spanner size across flats in decimal inches.

Metric equivalent


.117 inches.



.131 inches

3.33 mm


.152 inches



.172 inches



.193 inches



.220 inches



.248 inches



.282 inches



.324 inches (Probably the most commonly used BA size)



.365 inches



.413 inches


Application chart for some hub nut,ball joint sockets and box spanners etc (mainly older vehicles).
Our hub nut and ball joint sockets and spanners are listed on the relevant pages (ie) AF or SAE and BSW (Whitworth)
 3/4 inch af
 Common wheel nut size.
  Very common.11/16 AF commonly used on smaller.
(19mm equivalent )
  15/16 inch af
Wheel nuts
 Pre 1972 Land Rovers
 1 + 1/16 af 
Wheel nuts 
After 1972 Land Rovers.
 1 +1/4 inch af 
Rear hub nut
 Jowett Javelin
Virtually every nut and bolt on these vehicles is whitworth or BSF.
 1 + 5/16 inch af 6 point deep socket 
Front hub nuts.
 Mini,Austin  Allegro,Austin/Morris 1100  and 1300 Austin Maxi.

Front wheel drive hub nuts.Also cranshaft pulley and rear hub on MGB.

 1 + 1/2 inch  af.6 point deep  socket Front suspension ball joints  Mini,Allegro.Austin/Morris 1100 or 1300,Maxi.  Also fits Mini flywheel nuts.
  1 + 5/8 inch af
Rear Hub nut.
 BMC Midget,Austin Healey Sprite etc.

Probably other early BMC rear wheel drive A40 etc.

1 + 3/4 inch (socket or box)

Ball joints.

    Some early Leyland vehicles

    Socket must be deep type for ball joint application.

     1 + 13/16 inch af 6 point deep socket 

    Front suspension ball Joints

      Rover group Metro vehicles 
    Also ...Modern Triumph motorbikes?.

    Normally impact type.1/2 inch square drive.
     1 + 7/8 inch af
    Hub nuts
                    Older BMC (Wolseley 1500 etc).      Available as H/D box or socket.
     2 inch AF.

    Hub nuts

    Land Rover etc (used as substitute for 52mm)

    See list at foot of page.**

     2 +13/16 inch af
    Rear hub nuts
     Commer TS3
     Rear hub nuts.Front uses 42mm 
     2 +3/4 inch af 
    Hub nuts
    Bedford 2 Ton
     3 inch af 
    Hub nuts
    Bedford 3 Ton
    3 + 1/8 inch af 
    Hub nuts
    Leyland Roadrunner
      Also some IVECO trucks
    7/16 inch whitworth

      Scaffold Spanner

      Scaffold clamps.(with a pointed end the spanner is often called a 'podger spanner').
    Still often used but being replaced by metric.
    1 +1/8 inch whitworth
    Hub Nuts

    Morris Minor and other BMC vehicles

              Available as deep socket or box.
    1 +1/4 inch whitworth.
    Burman gearbox 

    (Panther,Vincent motorcyles and many others)

      Nearest equivalent 52mm as below.**
    22 mm deep
      Oxygen Sensor

      Modern vehicles

      Long socket often has 'window' in side.
     27 mm deep

     M24 threaded injector sockets.

    Most diesel injector sockets cars and light commercials..

    Will also fit some sensors.

    28mm deep

     HGV diesel injector sockets 

     Larger diesel injector sockets on many HVG engines.
     52mm six sided socket  
    Hub nut **
      Some models Land Rover and Range Rover
    close equivalent is 2 + 1/16 inch af.
     56mm (usually 12 sided)
    Hub nut

     Ford Transit 1993 onwards.

    Usually 3/4 drive.

     65 mm (usually 12 sided) 
    Hub nut

    Ford Transit (before 1993)

    Ford Transit models 130,150 and 190 plus some IVECO.
     50mm Eight sided
    Hub nut

    Austin A55,MGA.MGB*

    Note these are octagonal (eight sided).*
     56mm Eight sided
    Hub nut

     J2 Van and some early taxi cabs*

     As above (eight sided).*
    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 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.Note that both a set of whitworth spanners or sockets will cover both the whitworth standards (pre and post war) and the BSF ranges you do not (as some 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
    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
    0.551 inches = 14mm
    0.563 inches = 9/16 inch AF
    0.591 inches = 15mm
    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 (uncommon metric 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
    0.813 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 chromed 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 US,block spanners is another term for obstruction spanners 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.
    Links to to other pages on the Baconsdozen imperial tools web site are below.

    AF (SAE) sockets and spanners
    Servicing and repair
    BSF and Whitworth tools
     Home page.

    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).

    Baconsdozen Imperial tools

    Tel (44) 01493600718.

    Ordering and contact details click here.