Countryboy1

Hi, tried Googling for this, but still baffled!
I have a set of feeler gauges each marked 2,3,4,5,6,8,10,12,15 & 20.
I am trying to set some spark plug gaps which require 1,02mm or 0.040 inch.
What on earth do the markings on the each gauge stand for and which should I use please to achieve the correct setting? After each number neither mm or inch are indicated.
I'm guessing a combination of gauges 20,15,5 would get me 0.040 inch, is this correct? Or are the numbers MM and If so how do I achieve 1,02?
Any advice appreciated.
Thanks.

Grebo

Numbers don't make sense, they could be imperial, but missing some numbers go & buy a metric set from the chinese shop.
Metric starts with 0.05 up to 1.00



Suzi

Countryboy1

Perhaps good advice! Although the numbers must have made sense at some time!
Thanks.

Brian

Garbatellamike

Brian imperial feeler gauges used to be measured in thousanths of an inch and that is most likely what the numbers refer to imho but it has been more than 30 years since I last used them.....

Countryboy1

Mine are very old ones, so I guess they are imperial, but it would be nice if it said "inch" on each blade. Perhaps they are so old it wasn't deemed necessary!
Thanks again.

VFR

As Mike has said they are in thousants so just add the numbers up to 40 & they are the fellers you need.

Countryboy1

Thanks for that. Much appreciated & to all who responded.

snikpoh

There are no number missing - you simply use two 'leaves' to make the 'missing' number.

For example - 7 is not there so use the 2 and the 5.

Yes, they are in thousandths of an inch.

Countryboy1

Thanks, I'd realised the need to add together certain numbers to make another! Believe it or not I was an engineer many, many years ago and it's a long time since I've picked up feeler gauges for spark plug gaps.
It's confirmation of them being thousands of an inch that's helped.
Thanks again.

Fredbargate

Normally there is a clue somewhere on the feeler or the cover and occasionally they have thous on one side and the nearest metric equivalent on the other side.

Countryboy1

Thanks for that, but mine don't. Pretty sure now they are thousands of an inch which is fine.
Thanks again.

Fredbargate

Mine usually end up too rusty to read

Garbatellamike

lightly oil them Fred - shame on you

Fredbargate

I do/ did

But it's not red rust

They seem to get a sort of black patina? that makes it impossible to read the figures.

However from the above query about metric / imperial I note that in Europe most measuring instruments ( tape measures, depth gauges , feeler gauges ) are metric whist in the USA they are imperial.

But in good old UK they are bilingual unlike the population

Countryboy1

Well, done the job and replaced the six spark plugs. All going smoothly until number four which I unscrewed but the plug didn't extract with the plug spanner. After a moments studying why, I realised that the rubber ring inside the plug spanner which is supposed to grip the plug in order to assist its removal was missing! Must have remained around plug number three!
Anyway it needed a pair of long scissors to grip the undone remaining three to remove them.
Why aren't these rubber rings inside the spanner glued in place so they don't stick to the plug?
Anyway job seems to be OK as engine starts well enough. Will tell more when I take it out for a run!