Spark plug socket size }:-/

[^woody^]

Why is it that a 14mm socket is not actually 14mm, and a 14mm socket with a hex shape is bigger than a 14mm socket for a bi-hex (star) shape nut - which is actually 8mm on this same scale as hex sockets.

And no, I'm not drunk.

I was about to tell the bloke at the shop that all his plug spanners and sockets were mis-labeled!

 

[JohnD]

The size you mention is used for nuts whose heads are measured across the flats (AF). A open-ended spanner has the jaws (about) as far apart as the flats on the nut of bolt-head.

A 14mm open-ended spanner has the jaws (about) 14mm apart to grip the flats.

A ring or socket spanner does not grip the flats, it grips the corners

The corners are further apart than the flats.

 

[Burnerman]

One of the great mysteries of life!
Spark plugs are gauged by their thread diameter, the common ones being 18, 14, 12, 10 and 8mm. The threads are metric fine.
To confound things, old UK plugs are imperial, as are USA varieties.
The hexagon to undo them is also metric (with the above exclusions) and the size can vary with the manufacturer. As an example, a 14mm threaded plug will have an across flats size of either 16mm or 21mm. A 10mm plug is nearly always 16mm a/f.
John

 

[EddieM]

Well you learn summat everyday, not sure if it'll ever come in useful for me, but hey ho!

 

[^woody^]

One of the great mysteries of life!
Spark plugs are gauged by their thread diameter, the common ones being 18, 14, 12, 10 and 8mm. The threads are metric fine.
To confound things, old UK plugs are imperial, as are USA varieties.
The hexagon to undo them is also metric (with the above exclusions) and the size can vary with the manufacturer. As an example, a 14mm threaded plug will have an across flats size of either 16mm or 21mm. A 10mm plug is nearly always 16mm a/f.
John

My head just exploded

 

[^woody^]

The size you mention is used for nuts whose heads are measured across the flats (AF). A open-ended spanner has the jaws (about) as far apart as the flats on the nut of bolt-head.

A 14mm open-ended spanner has the jaws (about) 14mm apart to grip the flats.

A ring or socket spanner does not grip the flats, it grips the corners

The corners are further apart than the flats.

The socket I was referring to is a hex, just the same shape as the nut so I presume it should be guaged the same by across the flats, not corner to corner, and should be referred to by the same dimension as a spanner.

Even so, its stated as 14mm and is not 14mm across the flats or corner to corner! Whats wrong with these engineers?

 

[JohnD]

If it was a ordinary Metric spanner, it would be described as 14mm to fit a nut that was 14mm across the flats. That's how metric spanners and nuts are defined. It is much more simple and straightforward than other definitions.

Find a bolt with a 14mm head and try it.

However, it now seems that you were looking at a spark plug spanner, that has fallen into the old trap of having a description that is not based on nut size or spanner size.

 

[^woody^]

However, it now seems that you were looking at a spark plug spanner, that has fallen into the old trap of having a description that is not based on nut size or spanner size.

Yeah, not only that but with the more modern thinner bi-hex plugs a normal deep 14mm bi-hex socket will fit a 14mm bi-hex sparkplug, but if I actually wanted a spark plug socket, they are refrred to as 8mm.

 

[Keithmac]

I come across this all the time at work, best bet is to have a new plug handy to size the tool up.

Year ago we used to service loads of Honda NC30's, they had tiny Er9eh9 plugs that were always prone to fouling and fronts were a swine to change.

I use bike plugs in my car BKR9EIX.

 

[Notch7]

its as annoying as BSP thread sizes.

1/4" 1/2" etc etc -refers to the internal pipe diameter not the thread.

And just when you think you've got it, you discover there are both straight and tapered threads

 

[Keithmac]

Same with AN fittings, makes no sense!.

 

[chainsaw_masochist]

 

[Nige F]

Mr. Gumby

 

[EFLImpudence]

Yeah, not only that but with the more modern thinner bi-hex plugs a normal deep 14mm bi-hex socket will fit a 14mm bi-hex sparkplug, but if I actually wanted a spark plug socket, they are refrred to as 8mm.

The same as bolts - 5mm. spanner/socket doesn't fit M5 bolts.

 

[^woody^]

The same as bolts - 5mm. spanner/socket doesn't fit M5 bolts.

M* always refers to the thread or shaft size and not the head, I'm ok with that - it's quite logical.

It's only when something is actually marked up as a 14mm socket but is not actually a 14mm socket but 16mm that I find my senses being assaulted.