Why are hex head bolts hex rather than Octagonal (or square?)

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They must have their own version of metric there. Any time I have to repair Chinese made junk none of the available metric items seem to fit. Usually end up drilling and tapping to do the repair.

Reply to
Steve W.
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Snowflakes....

-jc-

Reply to
John Chase

Does that mean that you need a lime and some nachos?

moT

Reply to
Tom Accuosti

A couple of things come to mind why hexagons might be chosen over other polygons.

Two parallel faces of larger flat dimension than an octagon. You can slide a wrench straight on from the side unlike twelve point aircraft stuff. A larger manufacturing tolerance on the head dimension and matching wrench dimensions because of the larger flats. Can reposition a wrench in a smaller increment than a square for tight quarters work.

Some blacksmith wanted to stand out in the manufacturing world making horse buggies. Forging parallel faces is pretty easy compared to pentagons and septagons.

Interesting question. Thanks

Tom Lipton

Reply to
tlipton2

You never looked on top of a fire hydrant did you? They use a five sided drive there to keep stupid people from opening the valve up.

Reminds me of a funny story... One afternoon I was outside working in the driveway. There's a fire hydrant half a block from my house, in great view. A fire truck pulls up to the hydrant (fire station happens to be about three blocks away from my house, too.) and three firemen hop out, one with a wrench in hand. They were just wearing blues, so I suspected they were going to drain the hydrant or something. They were taking it casual with this assignment, obviously. Idiot number one opens the valve without taking the cap off, so he closes it again. Idiot number two smacks the cap to spin it off. Idiot number three was standing about five feet away from the hydrant when the cap blows off from the pressure, snaps loose from the lanyard, and slams into the side of idiot number three's knee. While the first two idiots are thinking this was funny, the idiot number three hits the ground screaming bloody murder, sounding like he was in some serious pain. I had to walk back inside to prevent myself from laughing out loud at the collective stupidity of them all. Shortly after, another fire truck and an ambulance pulls up, completely blocking the intersection, and carts off idiot number three. I still don't think they've fixed that lanyard....

Reply to
carl mciver

One advantage to the pentagonal fire hydrant valve bolt is that its actual dimensions don't have to be particualarly precise since the wrench is an adjustable one.

The wrench has a screw-in handle that pushes against a flat to force the opposite angle into a "V".

Only 2 pieces and will fit any pentagonal bolt/nut up to 2".

Reply to
RAM^3

Try a Google images search for giants causeway

Reply to
Andy Webber

Snowflakes =/= rocks.

Jim

Reply to
jim rozen

Someone said "in nature" and didn't limit it to rocks, Jim.

Reply to
Dave Hinz

I'm trying to understand how that happened; i.e. where all that energy was stored, Carl.

The only thing I can come up with is that there must have been a good sized air pocket above the valve which got compressed by water pressure when the valve was opened and closed, 'cause I don't think just water or the hydrant/riser pipe by itself would store enough to do that.

Jeff

Reply to
Jeff Wisnia

In a big air pocket...

Exactly. Most hydrants over the last (insert bignum) years have the shutoff valve on a long temp which goes well underground - prevents freezing in that sort of climate. So the hydrant is dry for maybe (thinks) 6 feet of height at a 8" diameter. So, it's compressed to

50PSI (or whatever mains pressure is) once that valve is opened, which is quite a bit of force on a 6" hose connection.

Dave Hinz

Reply to
Dave Hinz

My inquiring mind just had to know...

How does the water drain out and the air get back in when it's time to close up and go back to the station?

Sure enough, there's a drain valve at the bottom of the hydrant which opens when the main water valve is closed. I expect they must put some crushed stone around the bottom to give the water someplace place to go.

This picture shows a hydrant with an automatic drain valve:

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That hydrant looks like it uses a toggle action driven by right/left threads on the valve stem to move the main valve sideways. Clever...

I wonder if they have to leave the cap off until they are sure the water has drained out to avoid creating an air lock?

Jeff

Reply to
Jeff Wisnia

That's a good question. Unfortunately the hydrants I have (long story, don't ask) are missing that end of the mechanism. I would assume there is some sort of a drain.

Oh good, you saved me a trip to google. Makes sense.

The ones I have just move the rod up/down, but they're ancient.

Dunno. We don't have hydrants in our department's area, our parties are strictly "BYOW".

Dave Hinz

Reply to
Dave Hinz

I've also heard of the "Italian Vernier."

Tape measure...

Regards,

Robin

Reply to
Robin S.

Hex head means 60 degrees between flats.A 15 degree offset open end wrench has 30 degrees of availability, depending which way you flip it, so you can turn the nut 15 degrees, flip the wrench, another 15 degrees, etc.as long as you have room for 15 degrees or more of rotation.

Reply to
nospam.clare.nce

Hydrants drain down when the valve at the bottom is closed. They're full of air most of the time - they'de freeze otherwise.

The energy was stored in the air, probably at about 50 psi, in a volume of pipe 6 feet long and 10 inches in diameter. It's a good thing he wasn't killed.

Jim

Reply to
jim rozen

I've never had the misfortune to see the Hydrant on my lawn in action but at least twice a year a PUC pickup comes and the driver takes the cap off and drops a rope in to check for water. Gerry :-)} London, Canada

Reply to
Gerald Miller

^^^^^^^^^^^^^^^^^^^ How about a "Polish sausage"?

Polish sausage.

Reply to
Leo Lichtman

A regular pipe wrench works fine to open hydrants. At least the ones I've opened, don't take much force to turn and no damage to the pentanut. And yes they drain from the bottom, if not open entirely a lot of water can escape out the bottom, potentially causing problems (drain closes when valve is fully open).

Eric

Reply to
curly

Depends on your point of view... a mineralogy book of mine states the most abundant mineral on earth is ice, covering 1/8 of the crust.

Quartz is mostly hexagonal, among a slew of other minerals. Zinc, magnesium and titanium, to list a few, are pure metals which crystallize HCP (hexagonal close-packed).

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

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