Why SAE spark plug sockets?

[Vinko]

Just curious:

On my 2000 BMW straight 6 the plugs take a 5/8's socket.

And I understand it, quite a few plugs in German (and Japanese) cars take or took SAE sockets.

What's the history around this? And why aren't they otherwise metric?

Is it only for vehicles exported to the US that the plugs take SAE? Or is this an international standard?

Thanks for the replies

 

[Valkyrie Rider]

Ive always wondered this myself. I've owned BMW, VW, Audi, Honda, Toyota as well as american vehicles, and not one has used a metric spark plug socket.

 

[Lump]

I think that the US spark plug manufacturers were world-dominant at one time, and it is likely that all the spark plug manufacturers got together and agreed upon standard sizes. Back in the 1920's and earlier, spark plugs were made of all different shapes and sizes, but sometime in the 1930's they all became very standard, size-wise.

Plus, World War II put literally millions and millions of US-made engines in countries all over the world, and when the war was over, most of them were left behind, and used by local citizens for peaceful means. Maybe that has something to do with it?

 

[nitropowered]

Its the same with wheels too. Wheel diameters are all done in inches, then combined with metric width.

There are few other weirdo SAE-Metric combinations I can think of. I think it has to do with war time in the early 1900s where the tooling was SAE, but they wanted to use metric. For example bicycle bottom brackets (where the cranks spin) are threaded SAE, but the width measurements are done in millimeters.

 

[gtivr4]

Also, 5/8 is pretty much the same as 16mm...

 

[sselander]

there are some spark pllugs that are 18mm
not that common

 

[porphyre]

Yeah... the factory service manual for my Japanese car specifically calls out a 16mm spark plug socket.

 

[HandyManny]

Yeah... the factory service manual for my Japanese car specifically calls out a 16mm spark plug socket.

Use 5/8ths

 

[gtivr4]

16mm = .6299
5/8 = .625

Ever notice that a lot of socket sets skip 16mm? Thats because 5/8 is close enough.

 

[Displaced Hokie]

My '83 Honda Shadow requres a 18mm spark plug socket. Nothing else will fit, and in fact a "regular" deep 18mm is too fat to fit down in there. Luckily the PO put a 18mm Craftsman spark plug socket in the tool kit.

 

[daveblank]

The new BMW's use a 14mm 12 point.

 

[malibu101]

The new BMW's use a 14mm 12 point.

I can understand the 14mm part
BUT
Is the spark plug a 12 point hex?
Just wondering.

 

[HandyManny]

16mm = .6299
5/8 = .625

Ever notice that a lot of socket sets skip 16mm? Thats because 5/8 is close enough.

There are a few SAE and Metrics that can be used interchangeablly. 21mm and 13/16ths, 3/4 and 19mm, 5/8 and 16mm, etc

 

[Eagle Point]

Sort of like why are the threads of the spark plug metric all these years??

 

[Lotek]

Most seatbelt bolts are SAE as well. 7/16 fine, was weird to find that on my 68 Porsche.

 

[justanengineer]

The wrench that fits the hex is irrelevant in measuring threads due to "close enough" tolerance that is only close enough until it causes you to ruin something.

Use a thread gage - threads are the only way to reveal if its a standard fractional or metric thread. I would be curious to know if these really are standard as opposed to metric threads since quite a lot of American made cars these days use a metric thread.

 

[lowbucktruck]

Interesting topic. Just for the record, my old 1984 BMW E28 straight-six plant (the M30 motor) also took an 5/8 socket for its spark plugs too. So BMW has been doing that for awhile.

 

[route246]

Maybe because in '68 those were retrofitted for US safety regulations or something?

Most seatbelt bolts are SAE as well. 7/16 fine, was weird to find that on my 68 Porsche.

 

[daveblank]

I can understand the 14mm part
BUT
Is the spark plug a 12 point hex?
Just wondering.

Yes I've been told that ath Nissan Sentra uses one too.

 

[joecon]

Most spark plug are sae hex (5/8 or 3/4) but metric thereds(14 or 18).

 

[Wrenches of Death]

And why aren't they otherwise metric?

The metric system was and still is the measurement system of choice for EVERY Communist regime on the planet. Pol Pot used only the metric system. Look where Cambodia ended up after that.

Just say NO! to the metric system.

You know, the thread diameter and thread pitch on those SAE spark plugs of which you speak is actually metric. And has been for many decades.

WoD

 

[Moose-LandTran]

Just curious:

On my 2000 BMW straight 6 the plugs take a 5/8's socket.

And I understand it, quite a few plugs in German (and Japanese) cars take or took SAE sockets.

What's the history around this? And why aren't they otherwise metric?

Ive always wondered this myself. I've owned BMW, VW, Audi, Honda, Toyota as well as american vehicles, and not one has used a metric spark plug socket.

They are metric, 16mm.

The new BMW's use a 14mm 12 point.

I think that's only certain engines, at least it has been in my experience. As far as i know, only N52/54/55 engines use those plugs.

I can understand the 14mm part
BUT
Is the spark plug a 12 point hex?
Just wondering.

Yes, they are 12-point plugs. Some other Euro cars use 14mm 12-point spark plugs, PSA-Peugeot-Citroen use them on some engines.

 

[gtivr4]

The metric system was and still is the measurement system of choice for EVERY Communist regime on the planet. Pol Pot used only the metric system. Look where Cambodia ended up after that.

Just say NO! to the metric system.

The metric system is the measurement system of choice for EVERY country but the US, Burma and Liberia.

 

[Moose-LandTran]

The metric system is the measurement system of choice for EVERY country but the US, Burma and Liberia.

Despite being English and therefore being obliged to hate everything French, i gotta say that the Metric System kicks ***!

 

[Steve_P]

Maybe because in '68 those were retrofitted for US safety regulations or something?

this is still true for all the Japanese (modern) cars I've owned; I assume it's one of those "it's been tested..." type things and it's easier to use the 7/16-20 than to go thru the certification for the metric size.

As far as dissing the metric system and associating it with our enemies, get real. We're the last major holdout in the world that stick with the retarded IPS system. Lettered and numbered drills? WTF? Sixteenths? Please. Drill size for a 7/16-20? Who knows w/o looking it up. drill size for a M10X1.5? Simple: 10-1.5=8.5.

 

[dieseldodge01]

I am pretty sure Honda motorcycles from the 70's or 80's used metric spark plugs. My dad had a HondaMatic and a Goldwing and has a 18mm sparkplug socket, I can't remember which bike he bought it for.

 

[KenS]

The same reason all metric countries use 3/8-inch ratchet wrenches.

 

[Vinko]

Interesting topic. Just for the record, my old 1984 BMW E28 straight-six plant (the M30 motor) also took an 5/8 socket for its spark plugs too. So BMW has been doing that for awhile.

I've got an M30 in my 1991 E34 535i as well.

 

[Vinko]

this is still true for all the Japanese (modern) cars I've owned; I assume it's one of those "it's been tested..." type things and it's easier to use the 7/16-20 than to go thru the certification for the metric size.

As far as dissing the metric system and associating it with our enemies, get real. We're the last major holdout in the world that stick with the retarded IPS system. Lettered and numbered drills? WTF? Sixteenths? Please. Drill size for a 7/16-20? Who knows w/o looking it up. drill size for a M10X1.5? Simple: 10-1.5=8.5.

I like 16ths, 32nds, 64ths. Esp. with drill bits.

I also think Torx are for commie pinkos as well.

 

[Vinko]

I know from experience that this bad boy doesn't use no soulless, uber-rational metric system plugs.








God Bless America.

 

[Charles (in GA)]

As far as dissing the metric system and associating it with our enemies, get real. We're the last major holdout in the world that stick with the retarded IPS system. Lettered and numbered drills? WTF? Sixteenths? Please. Drill size for a 7/16-20? Who knows w/o looking it up. drill size for a M10X1.5? Simple: 10-1.5=8.5.

And just how would I know the drill size for the metric fastener without looking it up?

Charles

 

[Wrenches of Death]

I know from experience that this bad boy doesn't use no soulless, uber-rational metric system plugs.

I haven turned a wrench on anything as old as that Buick in a while.

Actually, if it uses AC number 45 or 46 spark plugs, the thread diameter and thread pitch ARE metric. Sorry.

That "4" in the AC number signifies 14mm.

See! No one believed Joe McCarthy. Now we can all see there really was a Communist conspiracy even back in the early 1950's to crush this country with the metric system.

WoD

 

[mikevango]

I know from experience that this bad boy doesn't use no soulless, uber-rational metric system plugs.








God Bless America.

You got to use a 21.3 mm socket to get them plugs out. Right?

 

[Moose-LandTran]

this is still true for all the Japanese (modern) cars I've owned; I assume it's one of those "it's been tested..." type things and it's easier to use the 7/16-20 than to go thru the certification for the metric size.

On all the Euro cars i've removed seatbelts on the bolts were metric. I still have a few at work.

 

[MattT]

On all the Euro cars i've removed seatbelts on the bolts were metric. I still have a few at work.

Yeah but you're in England and metric seatbelt anchors will be approved over there. They might not be here because the commie infiltration isn't as advanced this side of the pond.

 

[vssjim]

I know from experience that this bad boy doesn't use no soulless, uber-rational metric system plugs.








God Bless America.

I thought those used 10mm spark plug threads and 1950's Olds motors used 100 exhaust valve stms

 

[vssjim]

13/16's us really 20.8 mm and in real old engines 7/8" thread was common and Maytag used 1/2 pipe thread plugs.

 

[Wrenches of Death]

I thought those used 10mm spark plug threads and 1950's Olds motors used 100 exhaust valve stms

I'm don't ever remember messing with anything GM made after WWII that didn't use the standard old 14mm spark plugs.

I haven't done a value job on an automobile in thirty years. When they hardened everything up to handle the lack of cushioning of the low lead and no lead gasoline, it did wonders for the valves.

WoD

 

[Jbullfrog]

And just how would I know the drill size for the metric fastener without looking it up?

Charles

It is basic math: subtract the thread pitch from the size of the fastener. However, if you look at your Hansen derived taps, they call for standard drill bits in letter sizes.