Wiki: Size conversion

[meow2222]

Another one for your perusal....

Size conversion

A printed list of the exact metric sizes of imperial spanners, sockets & drill bits is handy. This is because some imperial tools make a good fit for metric nuts/bolts/etc, and vice versa (though of course many don't). A good example is 3/4", which is 19.05mm. A size conversion list can be stuck to the lids of sockets, spanners & drill bit boxes.

Such a list

• saves needing to find a spanner/socket/drill bit already in use

• provides 2 of the same size tool for some sizes, which is occasionally very useful

• enables old imperial tools to replace missing metric ones

• avoids need to buy replacements sometimes

• enables some metric tools to be used on old imperial equipment.

• enables purchase & use of now very cheap old imperial tools

• effectively expands your metric drill bit collection to include fractional mm sizes

This is definitely '''not''' a recommendation to use the sizes of socket & spanner that don't fit well. Doing so can damage nuts & spanners, and injure hands when the tool slips off.

==Size table==

64ths Inch mm Fits 1/64 0.40 2/64 = 1/32 0.79 3/64 1.19 4/64 = 1/16 1.59 1.5 5/64 1.98 2 6/64 = 3/32 2.38 7/64 2.78 8/64 = 1/8 3.12 3 9/64 3.57 10/64 = 5/32 3.97 4 11/64 4.37 12/64 = 3/16 4.76 13/64 5.16 14/64 = 7/32 5.56 5.5 15/64 5.95 16/64 = 1/4 6.35 17/64 6.75 18/64 = 9/32 7.14 7 19/64 7.54 20/64 = 5/16 7.94 8 21/64 8.33 22/64 = 11/32 8.73 23/64 9.13 24/64 = 3/8 9.52 9.5 25/64 9.92 26/64 = 13/32 10.32 27/64 10.72 28/64 = 7/16 11.11 11 29/64 11.51 30/64 = 15/32 11.91 31/64 12.30 32/64 = 1/2 12.7 33/64 13.1 34/64 = 17/32 13.49 35/64 13.89 36/64 = 9/16 14.29 37/64 14.68 38/64 = 19/32 15.08 15 39/64 15.48 40/64 = 5/8 15.87 41/64 16.27 42/64 = 21/32 16.67 43/64 17.07 44/64 = 11/16 17.46 17.5 45/64 17.86 46/64 = 23/32 18.26 47/64 18.65 48/64 = 3/4 19.05 19 49/64 19.45 50/64 = 25/32 19.84 51/64 20.24 52/64 = 13/16 20.64 53/64 21.03 54/64 = 29/32 21.43 55/64 21.83 56/64 = 7/8 22.22 22 57/64 22.62 58/64 = 29/32 23.02 59/64 23.42 60/64 = 15/16 23.81 61/64 24.21 62/64 = 31/32 24.61 63/64 25.0 64/64 = 1" 25.4mm 25

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.

==What size is ok?== ===Sockets & spanners=== It may be helpful to first explain that spanners and sockets aren't actually the size marked on them. Rather they're a size which will fit over nuts of the marked size. A slight degree of slack between tool and nut is required, otherwise spanners would often not fit on, and would often be an impractically stiff fit. So tools are already calculatedly oversize.

The question then is how much oversize is ok. And its not simple to answer. There should be just a little free play between tool and nut. If the gap is too big, the tool can damage the nut and slip off under pressure. The acceptable gap also depends on the nut size, for example a difference of 1mm is ok on a 1" nut, but entirely non-functional on a 3mm nut.

Perhaps someone will come up with an engineering table for safe gap limits some day. Until then I can only say that if there is any noticable amount of rotation of the tool relative to the nut, its no good, so the acceptable tolerances are fairly small.

===Drill bits=== With some jobs, drill bit size must be precise. But for most DIY this is far from true, and simply selecting the nearest size is usually absolutely fine. Thus more or less all imperial drill bit sizes are good for re-use in a metric world.

Size is critical when drilling a hole in metal that will be tapped, and close substitutes should never be used for this.

==BSW, Whitworth etc== Hopefully another list will be produced at some point to cover BSW & Whitworth tools. Some of us still have these old tools, and a percentage are perfectly good for re-use on metric equipment.

==Labelling== If you want to use old tools as a regular part of a set of metric tools, remarking them in mm makes life easier. Painting sizes on tends to wear off in use, it doesn't work well. A good option is a [[die grinder]] fitted with any small abrasive tool, which can be used to write on metal like a pen. Another option is to paint the whole outside of the spanner/socket/etc, and put a blob of that colour paint on the hole where it fits in the toolbox. (Each size uses a different colour [[paint]].)

==See Also==

• [[Spanner]]s

• [[Spanner|Sockets]]

• [[Drill Bits]]

• [[Special:Allpages|Wiki Contents]]

• [[Special:Categories&limit=200&offset=0|Wiki Subject Categories]]

[[Category:Tools]] [[Category:Save Money]]

NT

[Tim S]

[e-mail] coughed up some electrons that declared:

What about Whitworth (I've got some!)? Aren't they supposed to be even closer to metric on some sizes?

I could measure mine, but I'll have to find them first :)

Cheers

Tim

[meow2222]

Latest version...

Size conversion

A printed list of the exact metric sizes of imperial [[spanner]]s, sockets & drill bits is handy. This is because some imperial tools make a good fit for metric [[nuts]], [[bolt]]s, etc, and vice versa (though of course many don't). A good example is 3/4", which is

19.05mm. A size conversion list can be stuck to the lids of sockets, spanners & drill bit boxes.

Such a list

• saves needing to find a spanner/socket/drill bit already in use

• provides 2 of the same size tool for some sizes, which is occasionally very useful

• enables old imperial tools to replace missing metric ones

• avoids need to buy replacements sometimes

• enables some metric tools to be used on old imperial equipment.

• enables purchase & use of now very cheap old imperial tools

• effectively expands your metric drill bit collection to include fractional mm sizes

This is definitely '''not''' a recommendation to use the sizes of socket & spanner that don't fit well. Doing so can damage nuts & spanners, and injure hands when the tool slips off.

==Size tables== ===AF=== Most imperial sockets & spanners are measured AF, across flats. These are marked with the size, and no following letters. Conversion is a straightforward inch to mm conversion. ____ / \ AF means from / \ top to bottom \ / on this diagram \____/

64ths Inch mm Fits 1/64 0.40 2/64 = 1/32 0.79 3/64 1.19 4/64 = 1/16 1.59 1.5 5/64 1.98 2 6/64 = 3/32 2.38 7/64 2.78 8/64 = 1/8 3.12 3 9/64 3.57 10/64 = 5/32 3.97 4 11/64 4.37 12/64 = 3/16 4.76 13/64 5.16 14/64 = 7/32 5.56 5.5 15/64 5.95 16/64 = 1/4 6.35 17/64 6.75 18/64 = 9/32 7.14 7 19/64 7.54 20/64 = 5/16 7.94 8 21/64 8.33 22/64 = 11/32 8.73 23/64 9.13 24/64 = 3/8 9.52 9.5 25/64 9.92 26/64 = 13/32 10.32 27/64 10.72 28/64 = 7/16 11.11 11 29/64 11.51 30/64 = 15/32 11.91 31/64 12.30 32/64 = 1/2 12.7 33/64 13.1 34/64 = 17/32 13.49 35/64 13.89 36/64 = 9/16 14.29 37/64 14.68 38/64 = 19/32 15.08 15 39/64 15.48 40/64 = 5/8 15.87 41/64 16.27 42/64 = 21/32 16.67 43/64 17.07 44/64 = 11/16 17.46 17.5 45/64 17.86 46/64 = 23/32 18.26 47/64 18.65 48/64 = 3/4 19.05 19 49/64 19.45 50/64 = 25/32 19.84 51/64 20.24 52/64 = 13/16 20.64 53/64 21.03 54/64 = 29/32 21.43 55/64 21.83 56/64 = 7/8 22.22 22 57/64 22.62 58/64 = 29/32 23.02 59/64 23.42 60/64 = 15/16 23.81 61/64 24.21 62/64 = 31/32 24.61 63/64 25.0 64/64 = 1" 25.4mm 25

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.

===Whitworth=== 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 systems, known as:

• W (Whitworth)

• BSW (BS Whitworth)

• BSC (British Standard Cycle)

• BSF (British Standard Fine thread)

BS and BSW sizes are often seen on old tools. In some countries they're still in common use, and Whitworth is still used here for some niche applications.

Whitworth sizes are not Across Flats measurements.

Whit BSW/BSF Inch AF mm

1/16 W - 0.256 6.90 3/32 W - 0.297 7.54 1/8 W 3/16 0.340 8.64 3/16 W 1/4 0.445 11.30 1/4 W 5/16 0.525 13.34 (Camera tripod mounting) 5/16 W 3/8 0.600 15.24 3/8 W 7/16 0.710 18.03 7/16 W 1/2 0.820 20.83 1/2 W 9/16 0.920 23.37 9/16 W 5/8 1.010 25.65 5/8 W 11/16 1.100 27.94 11/16 W 3/4 1.200 30.48 3/4 W 7/8 1.300 33.02 13/16 W 15/16 1.390 35.31 7/8 W 1. 1.480 37.59 1. W 1.1/8 1.670 42.42 1.1/8 W 1.1/4 1.860 47.24 1.1/4 W 1.3/8 2.050 52.07 1.3/8 W 1.1/2 2.220 56.39 1.1/2 W 1.5/8 2.410 61.21 1.5/8 W 1.3/4 2.580 65.35 1.3/4 W 2. 2.760 70.10 1.7/8 W - - 76.70 2.1/4 3.150 80.01 2. W 2.1/2 3.550 90.17 2.3/4 3.890 98.81 3. 4.180 106.17 3.1/4 4.530 115.06 3.1/2 4.850 123.19 3.3/4 5.180 131.57 4. 5.550 140.97 4.1/2 6.380 162.05

===BA===

BA Inch AF mm

8 BA 0.152 3.86 7 BA 0.172 4.37 6 BA 0.193 4.90 5 BA 0.220 5.59 4 BA 0.248 6.30 3 BA 0.282 7.16 2 BA 0.324 8.23 1 BA 0.365 9.27 0 BA 0.413 10.49 = 7/32 BS

==What size is ok?== ===Sockets & spanners=== It may be helpful to first explain that spanners and sockets aren't actually the size marked on them. Rather they're a size which will fit over nuts of the marked size. A slight degree of slack between tool and nut is required, otherwise spanners would often not fit on, and would often be an impractically stiff fit. So tools are already calculatedly oversize.

The question then is how much oversize is ok. And its not simple to answer. There should be just a little free play between tool and nut. If the gap is too big, the tool can damage the nut and slip off under pressure. The acceptable gap also depends on the nut size, for example a difference of 1mm is ok on a 1" nut, but entirely non-functional on a 3mm nut. Steel nuts are more tolerant of oversize tools than brass. And the acceptable oversize also depends on the torque to be applied; at very low torque levels large amounts of oversize are ok.

Perhaps someone will come up with an engineering table for safe gap limits some day. Until then I can only say that if there is any noticable amount of rotation of the tool relative to the nut, its no good, so the acceptable tolerances are fairly small.

The one exception to that is where the torque applied is very low. If a socket is to be rotated directly by hand, with no bar, then generally anything that even loosely fits will do.

===Drill bits=== With some jobs, drill bit size must be precise. But for most DIY this is far from true, and simply selecting the nearest size is usually absolutely fine. Thus more or less all imperial drill bit sizes are good for re-use in a metric world.

Size is critical when drilling a hole in metal that will be tapped, and close substitutes should never be used for this.

==Labelling== If you want to use old tools as a regular part of a set of metric tools, remarking them in mm makes life easier.

Painting sizes on tends to wear off in use, it doesn't work well.

A good option is a [[die grinder]] fitted with any small abrasive tool, which can be used to write on metal like a pen.

Another option is to paint the whole outside of the spanner/socket/ etc, and put a blob of that colour paint on the hole where it fits in the toolbox. (Each size uses a different colour [[paint]].)

==Issues== Some vehicles use a mixture of bolt systems by design. Land Rovers are known for this.

Until 1955 Morris and MG used metric bolts with their heads ground down to fit Whitworth sizes.

==See Also==

• [[Spanner]]s

• [[Spanner|Sockets]]

• [[Drill Bits]]

• BSW, some issues]

• [[Special:Allpages|Wiki Contents]]

• [[Special:Categories&limit=200&offset=0|Wiki Subject Categories]]

[[Category:Tools]] [[Category:Save Money]]

[Dave Plowman (News)]

I'm not sure this is correct. I remember overhauling an MG XPAG engine and needing new big end bolts as the originals had stretched. And they had a very fine thread. I was told Morris used cycle threads on their bolts because they started out as cycle makers and had the tooling to make bolts etc so used that when they made cars.

[Tim S]

Cool - thanks :)

Nice wiki - very informative

Cheers

Tim

[e-mail] coughed up some electrons that declared:

[Kevin Poole]

Nearer, but not quite:

Morris and MG engines used a fine metric thread, e.g. M8 x 1.0, with nuts and bolt heads made (not ground down to) BSW sizes. This was originally because Morris bought engines from Hotchkiss, a French company with an engine plant in Coventry. There are many butchered threads where 5/16" UNF (7.94mm, 1.06 pitch) has seemed close enough (at first) to 8mm x 1mm.

There were 9 different thread types on my first MG - 6 original (BSW, BSF, mad metric, BSB, BSP, BA), and three intruders (UNC, UNF, and ISO metric)

Rolls-Royce played a similar trick: their 2BA nuts and hex head screws were 0.338" A/F, so that a 1/8" Whit spanner could be used. 2BA should be 0.014 smaller. Their 5BA nuts were oversize, too.

There's a rather better table than the proposed wiki list at

[Dave Plowman (News)]

Why then would Morris continue to use the same threads when they started making their own engines? My version makes more sense - they already owned nut and bolt making equipemt

The story I gave came from my father who was an apprentice in the motor trade just after WW1.

The big end bolts in question were extremely fine threads - nothing close to UNF. The torque setting was something very low like 20 lb.ft.

That sounds about right. ;-)

Interesting. I had an old Bentley with left hand thread wheel nuts on the nearside - mostly stripped when I bought it and fiendishly expensive to replace.

[Kevin Poole]

Morris first of all took advantage of Hotchkiss having spare capacity at the end of the Great War and bought engines from their Coventry factory extremely cheaply, then in 1923 bought Hotchkiss and formed Morris Engines Ltd

The story I gave came from my father who was an apprentice in the motor

M8x1. Mains were M12x1.5

£10.51 each, to you, sir. It's prices like those which enable me to justify charging so much for a wedding with the Silver Wraith.

Working now - I suspect some big DNS problems somewhere yesterday, since the met office disappeared for quite a while