Why do they skip sizes of metric combo wrenches?

[Ed Pawlowski]

What pattern? 8mm = .315 inches 5/16 = .3125 14mm = .5512 inches 9/16 = .5625

Close, but not equal. Competent tradesmen that work on both have both sets of tools.

[Terry Coombs]

 Even backyard hack mechanics like me have full sets of both .

[gfretwell]

If you have a worn 9/16 that 14mm will usually get a little better bite. Same with 1/2 and 12mm but you might be driving that one on. ;-)

[Clare Snyder]

Not true At all. The reason certain metric sizes are not included in most common tool sets is different countries use different metric standards which use different bolt head sizes. Japanese cars do not use 11 or 13mm heads - they use 10 and 12 - and

14 for 6, 8, and 10mm bolts. There are 3 main standards - ANSI/ISO, DIN, and JIS

All 3 use 7mm heads on 4mm and 8mm on 5 mm threads. All 3 use 10mm heads on 6mm, and DIN only uses 11mm heads on 7mm bolts.The other 2 standards do noy use any 7mm bolts. On 8mm bolts JIS uses 12mm heads while DIN and ANSI?ISO use 13mm. On 10mm bolts JIS uses 14mm, ANSI/ISO uses 16 and DIN uses 17mm. On 14mm JIS uses 19, ANSI/ISO uses 21 and DIN uses 22 On 16mm JIS uses 22 while ANSI/ISO and DIN use 24 Only DIN uses 18mm with a 27mm head while ANSI/ISO and JIS use 20mm threads with a 30mm head. Then there are some manufacturers who go it alone and put a 11 mm heads on a 6mm bolt.

SO for a german car you will get a set with 7,8,10,11,13,17,22,24 and

27mm. On a Japanese set you get 7, 8, 10, 12, 14, 19, 22, and 30mm On American metrics you use 7, 8, 10 (or sometimes 11), 13, 16, 21, 24, and 30mm

More or less.

[liddeljack62]

Also a metric socket set covering the same range as a 13 piece SAE set starting at 7/16 would requier 10 more sockets to be compleat.

[Ralph Mowery]

I fail to understand why there are wrenches that are sized so close to each other, not counting the need to fit bolts that should not be made either.

The SAE of going up 1/16 of an inch or less in sizes over 3/4 of an inch seems just as bad.

Does a bolt really have much more strength in size 21 than a size 20 in metric ? I would think that as wrenches/bolts reach around size 12 metric they would go up in steps of 3 to 4 to gain enough to make them worth while to make.

[TimR]

I'm with you. A lot of machines could use one size bolt versus 4 or 5. Some would be stronger than necessary but it would make repair a lot simpler.

[Clare Snyder]

7mm, 9mm 11mm and 13mm thread sizes are almost non-existant "in the wild" and in larger sizes the gaps ARE much larger, in the real world. The difference in head sizes per bolt size between "systems" makes the full size range important - not the 1mm incement in thread sizes.

[Clare Snyder]

A toyota car uses 4, 6, 8, 10 and 12 mm thread sizes with 8, 10, 14 and 14mm heads for almost everything, with the occaisional larger bolts where required. You would not want to use a 10mm bolt where most of the 4 and 6 mm bolts are used, I can assure you!!!!!

[Ed Pawlowski]

True, but it should have been settled 100 years ago. As long as the bolts exist the wrenches are needed.

[Ralph Mowery]

In the smaller sizes I can see it, but surely a 19 mm and 20 mm could just a 20mm and skip over the 19.

What would be wrong with using a 14 mm where the 10 mm is being used other than a very small cost.

[Clare Snyder]

Never seen a 19mm bolt. 19mm head? yes - but not a 19mm bolt. Might exist, but I've never seen one.\ Metric standards are 2.5, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 18, 20,

22, 24, 27, 30, 33, and 36mm in metric coarse threads. Metric fine are8,10,12,14,16,18,20,22 and 24mm M7 is VERY rare

[gfretwell]

The same is pretty much true of Yamaha outboards too. There are some

7MM (head) screws on the electronics and you need a 15MM to drop the foot. I bet 80% of the bolts have 10MM heads tho. Must be, that is the socket I lose most often ;-)

[gfretwell]

I had that discussion with IBM. We were carrying about 50 different Allen, Bristol 4&6 flute and Torx wrenches around to deal with basic screws. It got worse when they threw metrics at us. The answer was they buy assemblies from vendors and each vendor's engineer think they have the perfect fastener and none of them agree what it should be.

I then asked if we had bid specs. Couldn't we tell them what to use. The answer was no.

[Xeno]

Yes, works Ok one way but not so well the other.

Absolutely correct. In fact, I had 3 complete sets of tools since I needed the British sizes as well for the trucks I used to work on.

[Xeno]

I was going to mention that *difference* between Euro and Japanese but you beat me to it! Comprehensively so too! ;-)

[Clare Snyder]

Gotta love those BSF and BSW wrenches, eh? different wrench for 1/4" coarse and 1/4" fine thread - and neither one is the same as either an SAE inch or metric sized wrench - - - - -

[bobburr0311]

9mm needed for top nut on shocks of Dodge ram. Also, backing nut size 18mm.

[Clare Snyder]

Use your 9/32 wrench for the 9, An 18mm will work on an 11/16, but unless one or the other is badly worn you can't use an 11/16"nch on an

18mm bolt or nut.

I have several "full sets" that have everything up to 19, plus 22 and

24 -and one set with a 21.