I have a silly question. Why do you need both metric and standard? I have always used my metric sockets for everything and never had a problem. Is there really a need to have both?

 

Once you get over 1/2", metric and standard become very close in size. It's under 1/2" that you need the separate tools. But to do it right, you really do need full sets of both.

 

I you work on older stuff, it is all standard, newer stuff has a lot of metric, What I hate is working on something that has both. Looks like they could use all metric or all standard and not mix it up on the same vehicle or piece of equipment

 

Yeah, I always hated that too. Pretty much just on American vehicles that you see that. They've changed to metric pretty much completely these days, but for several years you had 'hybrids' because all the fasteners went to metric on the body, but they still used older engines with standards, and didn't want to re-tool or cause confusion.
btw, I use 13mm interchangeably for 1/2 all the time any more, and 5/16 - 8mm has no appreciable difference. All in all, you're better off with metric sets because they'll fit standards adequately most of the time, but it doesn't work nearly as well trying to go the other way.

 

Unfortunately, there still are some times that metrics won't work on standards, and standards won't quite work on metrics. 15mm is slightly larger than 9/16, but 14mm is slightly smaller, but works great on rusted up exhaust bolts that were originally 9/16, 5/8 and 16 mm don't quite work, 17mm and 11/16 aren't a perfect match, 18mm has no standard counterpart, 19 and 3/4 work well together, 20mm won't, 21 and 13/16 work well, then as you get bigger you can interchange ok. 7/16 doesn't interchange, 3/8 doesn't interchange,but the smaller ones will.The half size metrics take up the difference.

 

I agree with you we have couple of Cat D300E Series I haul trucks and then we bought a couple of 300E Series II haul trucks and the Series I are all standard and the Series II have both. And of course Cat has to be different instead of the normal metric 17mm and 19mm heads they use 16 and 18 mm heads and usaully when someone replaces them they use the normal metric head size. What really sucks is that they are basically identical trucks just different hardware. After a couple of trips to the tool box a guy has it figured just very annoying when you crawl up or into nice tight spot and you have the wrong wrench.

 

My Triumph TR7 had "standard" (not really, but some other UK standard, but used english units) bolts on the drivetrain, metric on the body (and holding the drive-train to the chassis)... what a picnic.

I found that 13mm is slightly bigger than 1/2", so if you have a well-worn 1/2" that'll do for 13MM in a pinch. 11MM is slightly smaller than 7.16". 16MM is 5/8". 17MM is slightly smaller than 11/16", 14MM is slightly smaller than 9/16", etc. You get the idea.

10mm, and smaller, 12mm, 18mm, and others are harder to find a near-match with English units.

But I do have complete sets of both...

 

Much of the older british stuff used a size called "Whitworth", I think a 3/4" whitworth bolt size refered to head size rather than bolt size, I think it is still used in several countries but is outmoded. I'm sure others here know much more about it than I do, I hope they chime in

 

Whatever the British thing was, most of the thread-pitches were finer than the American version.

However, the finer thread pitch was still something available as "American standard".

 

I agree that you can use the 'wrong' wrench type when things are easy. That is, metrics are often 'close enough'.

However, when you have to dig out your six points, and maybe 'extend' your ratchet handle to get things going ( after using liquid wrench, torch, etc.), then you better have the right size. With some luck, the stubborn thing will turn and not snap off.

Also, if you're doing tubing -- e.g. brake lines, you want the right one. That open section on a flare wrench is enough of a handicap, you don't need something just a touch too big.

But, if you do have a really rusted bolt, and the head is already mangled, you MIGHT be able to force a slightly smaller wrench on it, substituting metric for standard and vice versa.

As for Whitworth, this was an English standard that started out as a standard for the rifling in rifle barrels. Some English cars actually used metric, standard (SAE), AND whitworth on one vehicle!

I do believe that the size given was the head size. Bolts ( SAE and Whitworth) could NOT be interchanged, because the thread shape was slightly different, even if the pitch ( threads per inch) was not. The Whitworth thread shape was claimed to be superior, and possibly is. However, it's no longer used anywhere as far as I know.

ford2go

 

One metric size you have to have is 10MM. The SAE stuff just won't fit those fasteners.

 

The only difference between Whitworth thread, and American sharp-v thread is the profile of the threads. Sharp-v are just that the threads are sharp to a point, crest and root. Whitworth threads have a rounded crest and root. Once you get over a certain size (1 1/2" Dia ) they will interchange if they are the same pitch. Neither is any stronger than the other. Because the Whitworth thread had more contact area in the threads they will pull a gald more often if they are not properly lubricated.


Ryan

 

I once had a Norton motorcycle from the 50's, and it used Whitworth fasteners. Fortunately for me, the bike came with a set of Whitworth tools. When I sold the bike, I gave the guy the tools too. Guess what...they were Craftsman!

MR

 

Whitworth tools DOES have to do with the threads like they said, but during WWII the head sizes changed (tight spaces, conserving metal for the war effort, etc.) and the head size marked on a socket pre WWII would be different then the head size post WWII.