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View Full Version : Comparison of Metric and Standard sizes...


iiibdsiil
02-13-2006, 05:46 PM
Okay, so let's get some sort of a list going here of what sockets you can substitute for others. This may help someone trying to figure out if the speciality sockets or wrenches they want to buy should be in say metric so they only have to buy one set. For instance, ratcheting wrenches and swivel sockets.

I think most American cars started switching to metric in like 96 ish. My 96 Impala, half the stuff is metric and half the stuff is standard, and I just about ALWAYS use metric sockets on EVERYTHING. Of course, for like an old 'Cuda or something, you would want the speciality sockets and wrenches in standard.

Also, a box end wrench and sockets seem to not cause any problems when you are doing this, although, the open end on occasion seem to be too sloppy for my comfort.

So...

5/16 inch = 0.3125 inch = 7.9375 millimeter, so 5/16" would work for metric, and it most circumstances I believe the metric would work for the 5/16"

3/8 inch = .375 inch = 9.525 millimeter, so 10 mm works for both. With a quality 6 point socket for sure at least.

7/16 inch = 0.4375 inch = 11.1125 millimeter, so 7/16 definitely will work for 11 mm. I can't comment on this because I couldn't tell you what the head of the bolt/nut is SUPPOSED to be so I can't say 11 mm will work, but I don't think I've ever touched my 7/16. I may be wrong though.

1/2 inch = 0.5 inch = 12.7 millimeter, so 13 mm works for 1/2".

9/16 inch = 0.5625 inch = 14.2875 millimeter, so 9/16 works for 14 mm.

5/8 inch = 0.625 inch = 15.875 millimeter, so 16 mm works for 5/8". I believe many impact socket kits that include both standard and metric have only one socket for these two.

11/16 inch = 0.6875 inch = 17.4625 millimeter, so 11/16 would probably work fine for 17 mm if you were in a bind in where you didn't have another 17 mm socket. I think this is one of the circumstances where the open end wrench is too big for comfort.

3/4 inch = 0.75 inch = 19.05 millimeter, definitely a just fine and dandy substitute as I know most impact socket kits that include both metric and standard only label it as a 3/4/19 mm.

13/16 inch = 0.8125 inch = 20.6375 millimeter, so you could most likely use a 21 mm as a substitute.

7/8 inch = 0.875 inch = 22.225 millimeter, so a 22 mm would work for 7/8".

15/16 inch = 0.9375 inch = 23.8125 millimeter. 24 mm will work for 15/16" as I have done it many times before.

1" = 1 inch = 25.4 millimeter, again, that's going to be personal judgement on your part if that .4 mm is too much slack for you to be comfortable with.

Now, I'm probably going to get flamed for this post, as you should use the proper tools on the job. But, me personally, I don't worry about it on most of the ones I stated where metric should work for standard. If the bolt is super tight, I typically grab the correct socket, but I seldom have a problem with the heads on the bolts rounding even in the least. The bigger point here is that IF you are in a bind, here's a list of commonly used sizes that you can substitute back in forth. That bind may be you only have one 14 mm deep socket, and you need another at the same time, so you can save yourself buying a second socket at that inopertune time that you will probably never use again. For me, it's just out of sheer laziness. When I am under a car, whether on a lift or on jack stands, if I have the metric socket next to me, I'm going to use it so I don't have to waste time getting the right one. Great attitude, I know :)

I started out buying my upper level brand tools (above Craftsman) in metric. I was working on German cars at the time, so I didn't need standard sizes. When I worked on American cars, I seldom didn't have the complete set of sizes I needed. Honestly, it works fine most of the time, but every case needs to be judged on an individual basis on what you consider "tight enough". At the very least, you are pretty close, and it's not like you are trying to shove an allen socket into a torx head. I have a couple friends that's tool collections don't include Torx, and that is a very common thing they do.

Hope this helps someone out, and I am interested in hearing other peoples opinions on what works for what, or something you have had a problem with.

kartracer55
02-13-2006, 05:50 PM
1/2 wrench fits just about every 13mm hex I have ever encountered better than any 13mm tool. Its perfectly tight.

Jim

REFLEXX
02-13-2006, 06:10 PM
Metrinch - solves your problem!

http://www.mitools.com/info/

GearHead_1
02-13-2006, 07:28 PM
Though it may look good on paper, you won't find many people who make their living with tools that would agree with the printed version.

l_bilyk
02-13-2006, 07:36 PM
So what happens when you put a sockets that's a tenth oversize on a nut that's a tenth undersize becase some of it rusted away?

drbill
02-13-2006, 07:43 PM
The most common sizes that can be used are
5/16-8 7/16-11 1/2-13 9/16-14 5/8-16 3/4-19 13/16-21 7/8-22
They aren't perfect but they work.
I still think you will need both metric and standard sizes if you plan on using them much.
I can't tell you how many times I came across a stripped or rusted bolt/nut that required the use of a smaller size socket hammered on to remove it. An example of this would be a bad 1/2 bolt that you could pound on a 12mm socket and remove it.

Steve_S
02-13-2006, 09:52 PM
Sockets aren't that expensive, but removing a rounded off rusty old bolt can be. If you really can't find the right size, just use a Vari-Metric Compensator (http://s7.sears.com/is/image/Sears/00904450000?layer=comp&wid=190&hei=190&fmt=jpeg&qlt=75,0&op_sharpen=0&resMode=norm&op_usm=0.5,1.0,0.0,0).

oldgoat
02-13-2006, 10:19 PM
I made up a chart that gives the decimal size for a each metric size up to about size 24 or so. The one I remember the most is the 19 - 3/4. For me though I will try to use the correct metric size and if one doesn't fit because the head is a little rounded or undersize I will try a SAE. Also works the other way though. With metrics becoming the norm it doesn't make sense to try to get by without it. Just buy the basics and go from there.

ThreeBay
02-13-2006, 10:32 PM
The Vati-Metric Compensator made me laugh ... thanks :lol:

dink
02-14-2006, 09:25 AM
There was a topic in Grassroots Motorsports Magazine in the December 2005 issue...breaking down on the sizes to compare metric to SAE

filthy_shovel
02-14-2006, 10:47 AM
This list is useless. A good way to strip bolts is to use the incorrect socket/wrench size. It is also a great way to round off bolts. Any serious wrench will never do this.

Uncle Buck
02-14-2006, 10:52 AM
Years ago when I could not afford to add any metric stuff, some guy told me that from either 21, or 22 mm on up my standard sockets could serve double duty for metric, and as I recall he was right. Conversely 21, or 22mm and lower the standard sizes would not work on metric stuff. Anyway, you might check it out and see if that is true. Herb

Uncle Buck
02-14-2006, 11:08 AM
filthy shovel: Do not be so quick to rush to judgement! There must be some interest in discussing the idea, we're on page two!

filthy_shovel
02-14-2006, 11:51 AM
filthy shovel: Do not be so quick to rush to judgement! There must be some interest in discussing the idea, we're on page two!

My experience as an autotech regarding this is basically that there is no substitute from the correct wrnch/socket.

Yet it is true that you may find metric socket will fit better on a SAE nut (or vise versa) better, but that is usually a trial and error thing and not really as precise as what is in the list.

My days as an auto tech are plagued with working on cars with rounded nuts and bolts and also, young apprentices that would do exactly what is related in this thread.

GearHead_1
02-14-2006, 11:56 AM
My experience as an autotech regarding this is basically that there is no substitute from the correct wrnch/socket.

Yeah, what he said! :bowdown:


You can do it, but you can't make a living doing it. Sooner or later it will bite you in the butt.

Uncle Buck
02-14-2006, 12:03 PM
To actually try to half ass substitute standard for metric, or vise versa as a paid wrench would be deplorable! The only circumstance where this is tolerable in any way, shape or form is due to financial hardship, (not acceptable for paid wrenches) or something like being stuck on the road and a have to situation or the like. If you are a paid mechanic you should have the proper tools to do the job, or quit wrenching and find another line of work!