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8 mm socket vs. 5/16" socket

X

xroad

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If I buy a 8 mm socket and a 5/16" socket, would the 8 mm be sloppier and the 5/16" be tighter?

Possible that both sockets came out of the same production line and marked differently, one marked 8 mm, other 5/16"?

Maybe they sort them first before marking it? The loose ones marked as 8 mm and the tight ones marked as 5/16".

There are other similar sized sockets but not as close as 8 mm vs. 5/16". However, I suspect the others are made to the size it supposed to be.
 
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Fedwrench

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It would depend on whether you're using the 8mm on an SAE bolt or the 5/16 on a metric bolt.:bounce:

Seriously, I use metric stuff and don't have any problems except for usin 1/4 on 1/4 fasteners.
 
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xroad

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The manufacturer don't know what I am going to use the sockets for. 8 mm and 5/16" is so close in dimension, would the maker bother to make one a hair larger in size (or one a hair smaller)?
 
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Boiler

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The 5/16" will be sloppier. it is equivalent to 8.255 mm.

decimal equivalent to the fraction x 25.4 = metic size

or

metric size / 25.4 = fractional decimal equivalent
 
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xroad

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Boiler said:
The 5/16" will be sloppier. it is equivalent to 8.255 mm.

decimal equivalent to the fraction x 25.4 = metic size

or

metric size / 25.4 = fractional decimal equivalent
Click to expand...

5/16 in x 25.4 mm/in = 7.9375 mm

8 mm / 25.4 mm = 5.0394/16"
 
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xroad

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By calculation, I know which is SUPPOSE to be sloppier. Question is, did the manufacturer bother to make one a hair bigger or smaller? being that there are only 0.04/16" difference (that's 0.0625mm difference), by calculation.
 
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P

Prior

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8mm = 0.3149"
5/16= 0.3125"

So the 8mm will be a bit large on the 5/16" fastener, the 5/16" may be a bit small on the 8mm. With mfg tolerances for the fasteners, you can probably use either socket on either bolt.

www.joshmadison.com has a very cool conveter program you can download for pretty much any engineering conversion, which is very handy (does distrance, pressure, flow, area, torque etc)- great little program.
 
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xroad

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Prior said:
8mm = 0.3149"
5/16= 0.3125"

So the 8mm will be a bit large on the 5/16" fastener, the 5/16" may be a bit small on the 8mm. With mfg tolerances for the fasteners, you can probably use either socket on either bolt.

www.joshmadison.com has a very cool conveter program you can download for pretty much any engineering conversion, which is very handy (does distrance, pressure, flow, area, torque etc)- great little program.
Click to expand...

Thanks, but that was not my question. My question is a manufacturer question. What does the manufacturers do?
 
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mofo62

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Prior said:
8mm = 0.3149"
5/16= 0.3125"

So the 8mm will be a bit large on the 5/16" fastener, the 5/16" may be a bit small on the 8mm. With mfg tolerances for the fasteners, you can probably use either socket on either bolt.

www.joshmadison.com has a very cool conveter program you can download for pretty much any engineering conversion, which is very handy (does distrance, pressure, flow, area, torque etc)- great little program.
Click to expand...



Thanks Brother :thumbup:
 
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MattT

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I've got a couple 5/16" Snap-on FDP open ends I bought for use on 8mm. They are a noticeably tighter fit than any other correctly size open end I've ever used. This isn't a Snap-on or FDP specific anomaly because I've got quite a few in other sizes.
 
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xroad

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MattT said:
I've got a couple 5/16" Snap-on FDP open ends I bought for use on 8mm. They are a noticeably tighter fit than any other correctly size open end I've ever used. This isn't a Snap-on or FDP specific anomaly because I've got quite a few in other sizes.
Click to expand...

Do you have an 8 mm of the same brand, Snap-on FDP? If so, is the 8 mm open end looser on the same fastener?

If that is the case, that means Snap-on bother to make them different size, even though they are so close in measurement.
 
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Boiler

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Sorry for my 8.225 mistake. My piece of **** calculator didn't register me hitting the 1 in .3125. Of course I had to sit here and figure out what I did wrong....
 
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MrMark

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The OP had a great question, although I don't think anyone got it.

I have often wondered the same about 19 and 3/4, which is closer than 5/16 and 8 mm. The closest of all is 27 and 1 1/16 (only 0.5 thousandths or 5 ten thousandths, whichever way you like to look at it.)

I would bet although I haven't measured it that SO makes different broachings for the 5/16 and the 8 mm. The difference is fairly significant. It is 2.5 thousandths. You can feel that amount of play or slop. I don't know about the other two I listed. The 19 and 3/4 differ by 2 thousandths. The only one I consider truly interchangeable is the 27, of course.

I checked Armstrong wrenches vs. SO to see the tolerances and the SO were quite a bit tighter. In other words, the Armstrong 3/4 wrench, for example, will be 7 thousandths over while the Snappy is less than that. This is from memory so I may be a little off. I was surprised how much slop the manufacturers build in.
 
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M

MattT

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xroad said:
Do you have an 8 mm of the same brand, Snap-on FDP? If so, is the 8 mm open end looser on the same fastener?

If that is the case, that means Snap-on bother to make them different size, even though they are so close in measurement.
Click to expand...

I don't have an 8mm FDP because none of the FDP wrench series I wanted went below 10mm when I was buying off the truck. I do have a bunch of other FDP and regular SO open ends and none of them are noticeably tight like the two 5/16" FDP wrenches I have are on 8mm.
 
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logical

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I've never worked in a factory that made sockets but based on everything else i've been involved with, I doubt that a 5/16 socket comes from the same tooling as an 8mm socket.

Tooling wears out and sharing it between two sizes just means you replace or refurbish it twice as often....so there really isn't a "savings" to be had by sharing. It is much more likely that the manufacturing tools exist in "sets" just like they way sockets are typically sold.
 
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bsaint

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The only thing I can think of that is marked both 5/16 and 8mm is 5/16 plastic tubing. Like someone said, the difference between the two sizes as far as a machinist is concerned is too big to use the same tooling for both wrenches.
 
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Wakefield

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I like a nice tight wrench or socket as long as it will fit! I suspect that the amount of slop in some of them is more than the difference between the close sizes like 19mm and 3/4". Socket/wrench made just before old tooling that made it was taken out of service?
I wonder if the blueprint distance across opposite flats is(very slightly) less on a flank drive type socket than on the old sharp corner sockets when the sockets are both 6 point and the same marked size?
 
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