I suppose it depends on the size range and accuracy you need. At my level I use drill bits as slip gauges and mike them for the smaller holes. A pin gauge set would be an extravagance. I have telescope gauges for the larger holes and accept they can be a fiddle – or make a test gauge if I need to bore a fit.

I have calipers, internal telescope gauges and an internal mic, but with only one anvil so its range is a bit limited 3/4" to 1"! (I must make some anvils for it).

For smaller holes i use drill bits or turn a test diameter to fit. Where extreme accuracy isn't essential (i.e. I just want to get close before finishing to fit) I use a digital caliper internal jaws and add a fudge factor depending how small the hole is.

But as far as possible I try to avoid the need for accurately measuring holes.

Neil

A few months ago I had the opportunity to buy sets of HSS Drill blanks, 1-6mm and 6-10mm by 0.10mm increments for a very low price. Since having them have found they are very useful not only for hole diameters but also for measuring slots cut on the milling machine.

Emgee

I have an internal caliper dial type bore gauge, old but good, £3 at a boot fair.

Generally I use a pin or plug as already mentioned. I have bought a couple of dial bore gauges (not cheap) and used them when necessary. They take some time to set up but are particularly useful for measuring the taper, ovality etc of long holes such as cylinder bores.

[edit] If you making mating items, such as a bush and its housing or piston and cylinder, machine the bore first.

JA

Edited By JA on 13/12/2016 17:31:17

Small drill blanks used as plug gauges, as mentioned before tapered bore gauges.

Colin

For anything over 13mm I use Bowers 3 point bore micrometers. They are hellishly expensive new but I managed to pick up 3 for a reasonable price £80-£100 I think. I then collected odd ones off ebay and now can go from 13mm to 37mm in metric and from 1 1/2 inches to 4 inches in imperial. Well worth keeping your eyes open for them. Smaller holes I use various dowel pins, drill shanks and caliper guesswork.

David

Ball gauges below half inch, telescopic gauges above.

Just for idle amusement, here's a thought:

[assuming that it's a hole of known depth; either blind or through a plate]

Fill the hole with Wood's Metal and pare-it-off flush with the surface[s]

… some initiative may be required!

Then melt out the filler; weigh it; and do your sums.

MichaelG.

.

Yes, I know it's daft on several levels, but it might be useful.

Adding to off-the-wall ideas:

I think it'd be easier to tape one side of the hole and measure how much liquid fills it… allowing for the meniscus of course. For really tiny holes one could try and calculate the rate of capillary filling with different viscosity fluids and angle of fill. For really small holes how about finding the maximum amplitude of a signal that will pass through?

Really, and what do you base that pearl of wisdom on?

Tony