I attended the Uxbridge Auto Show yesterday after many years away. A really nice day out in a very friendly environment. Quite well managed too.
While looking at all the sellers I bought one 13 mm socket to use on my oil sump nut. It had flat not corner stucture which should make rounding off less lickely.
The question is, why did sockets that grip on corners ever become the mainstream, when ones that grip on the flat of a nut can't round the nut off.
Do corner sockets have any advantages?
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Twice as many starting points? Not much extra use, I agree, if used with a ratchet.
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I think it's one of those things that is only obvious after it's been invented. After all, if you were inventing something to turn a male hexagon, you would probably choose a female hexagon...
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Which is what you need for high torque application.
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My experience is that good corner sockets are less likely to round nuts off than cheap flat ones... where one doesn't work the other may. Then you have to get a new nut.
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Take a piece of paper and draw a hexagon - this represents your nut. Then take a piece of tracing paper and draw a second, fractionally larger, hexagon - this represents your socket. Then rotate the tracing paper a fraction until you simulate undoing the nut.
The entirety of the force is applied at the corners of the nut and tend to round them off. This is why female hexagons are not ideal and the engineers attempted to invent something more clever.
Replace the tracing paper hexagon with a dodecagon (with 12 sides - i.e. star shaped). Perform the same rotation to 'undo' the 'nut'. Instead of 6 points of contact - on the points of the nut - you have 12 points of contact. (To see this properly, exaggerate the shape of the socket, to make sure that it does make contact where I say it should; this is a part of the design of the socket.)
Best of all, these 12 points are on the flats of the nut, so much less likely to round the nut off. They are on the points of the socket. And the socket is made of a harder material than the nut. And the socket is disposable, whereas a damaged nut is disastrous.
So that is why you should buy a high quality 12-point star socket, not a 6-point socket.
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I am not certain if there is some confusion in the above posts as to 'corner' and 'flat' sockets.
Hexagonal sockets with flat sides grip on the corners of nuts and are bad.
Dodecagonal sockets with star sides grip on the flats of nuts and are good.
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A quote from wikipedia:
"Modern nuts and bolt heads are made with hexagonal gripping surfaces and as such limit the number of positions a wrench can adopt when placed over them. Sockets are produced in 6-point (hexagonal) and 12-point (double-hexagonal) configurations. When working in a confined area with limited turning space, 12-point sockets double the number of starting positions. 6-point sockets, however, offer a better grip on fittings and are less likely to slip and round off the corners with continued use and are generally preferred for damaged nuts and bolts."
If we are only talking about 6 or 12 point sockets, I would agree with the Wikipedia entry.
A usefull tip that has saved me a few times is to grind the end of the sockets down, this increases the amount of grip they have as the first part tends to be tapered to allow for an easy fit. Not sure if i've explained that very well, hopefully you will get the idea.
Wikipedia also explains (better than I can) the difference with an impact socket:
"High strength fasteners in demanding situations often require the use of an impact wrench or impact driver to deliver the amount of torque required to tighten or loosen them. Standard sockets are made of a strong, but brittle steel. When used with an impact wrench they can shatter explosively if they break. These sockets are made of a weaker, but more malleable steel that will deform and split instead of shattering. Impact sockets are not chrome-plated, as chrome can chip when used with impact wrenches. Instead, they are made with a coating of black oxide or a plastic coating to prevent corrosion."
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What you really want is "flank drive" sockets. They are available as either 6 or 12 point designs. The driving surfaces, instead as being flat as normal, are slightly convex so that as the socket is rotated to meet the hexagon the faces meet away from the corners. ie. on the flank. This design greatly reduces the likelihood of rounding the corners. The Halfords Professional 3/8" & 1/2" drive sockets are normally flank drive.
Andy
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What about sockets designed for impact drivers?
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Thanks for that moonshine. I guess if I'd engaged brain I could've found out for myself.
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IME having changed an elderly/worn set of double hexagon sockets for new hexagon sockets, I've stopped rounding the corners off very tight/rusty nuts and now shear the bolts instead.
I'd be inclined to agree with how the Wiki was when quoted above..
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I am impressed by the response. I rather agree with Moonshine. With a ratchet I can't see the 12 points v 6 points as being very important.
Has anyone rounded off with flats. It seems to me that vast areas of metal would have to be removed.
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If it is a very stuborn nut, but vital that you remove it undamaged, a good tip is to spend some time trying sockets from other series in the set to get a tighter fit. Sometimes by chance an AF size is a slightly tighter fit than a metric. I also agree about grinding down the rounded section of the socket. Aloso if the nut is rusty or already damaged it can be worth spending some time with a file reducing its size to the next available socket first.
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Filing a nut down to the next size - had to do that a couple of times over the years! Although I think most cars these days seem to use better quality bolts as I havn't had to do that since I found a rounded bolt on the brake caliper for an old 1990 Renault 19 we used to have.
Going back further, my first car was a 1972 Ford escort Mk2, I think the bolts on that came pre-rusted and rounded from the factory....
On second thoughts, maybe the reason for seeing less rounded bolts is that not so many people do DIY mechanics anymore?
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