Strange Plug Gauge Sizes?

Hi All,

This weekends car boot haul included a large selection of these plug gauges, all in very good condition but with very strange diameters.

I was expecting to see the normal .125, 250, 500 etc sizes but there are very few of those.

Are these for special applications of some sort?

There are many more smaller sizes as yet un-measured!

Cheers, Martin

.531 and .625 are imperial fractional sizes and most others will give metric sizes if you measure with metric tools.

.985 = 25mm

0.905 = 18mm

etc

Edited By JasonB on 03/05/2021 16:04:33

Don't rely on gauges being standard sizes, in production environment gauges are made to suit the process. Gauges are made to suit pre finish sizes, say for a drilled hole prior to finishing where the hole is a non rounded size.

Hi Jason, Many thanks, I was just assuming all were Imperial!

I made .985" come to 25mm! Typo I guess..

Are these gauges made to be just very, very slightly under their nominal size for some reason?

They seem like very useful things to have around when boring etc,

I think I will keep these and make a numbered case for them.

Cheers, Martin

Martin, gauges are usually made to be a push fit meaning that they will be very slightly undersize because if they were dead size you would need a press to insert them.

Brian

As Howard says, these are most likely to suit a process.

You wouldn't believe the amount of "odd" size gauging I've used over the years!

Jim

Yes a typo will correct it.

What did you measure with? as 3 decimal places may not be accurate enough as the difference between exact metric and just under is a couple of tenths.

There are hardly any "odd sizes" if you convert them, just a mix of whole mm and 32nd imperial.

Edited By JasonB on 03/05/2021 16:18:05

Maybe go/no-go gauges (incomplete set)

Hi Jason,

Just measured with a clean cheapo digital vernier caliper so not that accurate.

Will try a micrometer tomorrow.

Nice find though for £2! Got a box of broaches as well which seem very clean but some are a bit big for my kit.

The guy was selling some huge angle plates that I could never ever lift, God knows how he thought they would go at a car boot!

Thanks for the help guys, much appreciated.

Martin

Thanks for the numbers Jason, a big help! Martin

If you have the kit, it may be worth setting up a clock with slip gauges and rolling each gauge under the clock (Using it as a Comparator )

That should allow you to measure each gauge more accurately. It will also allow you to check that thre is no taper along the length.

Howard

At work, we had thousands of gauges in the stores, all sizes, and every one of them was returned to the inspection department for re certifying before being returned to the stores.