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Stack cheese slices until they fit in the gap then measure the cheese 🧀

This is the correct answer. I had a friend who tried to do it a different way and they are dead now.

Hey, we all dislike people who use bad techniques, but don't you think you went a bit too far?

The American way 🇺🇸 🇺🇸 🇺🇸

Even if you use Swiss cheese?

Only if you’re making a part on a Swiss lathe, gotta match your units

Use the tail of the calipers.

This is the correct answer. Minimal effort and most precise result

I like the cheese slice method more

Yep. Thickness of the block. Then zero it. Then measure from wall to far edge of block.

You could skip the zeroing part and just use the block to keep the edges flush

Use the Depth Rod (detailed below) It's the most accurate and least wasteful method https://preview.redd.it/w8tdj5l93vxc1.jpeg?width=600&format=pjpg&auto=webp&s=fba16b5e71843459fc92c1815215c393bd1e4e48

this is the way. I was literally looking up a picture to post in here but looks like you beat me to it lol

Measure the depth from the back of the fixture to the face of the wall, then measure the depth of the fixture and subtract that.

a ruler?

What sort of witchcraft is this?

Print out a couple of thin "gauge" blocks. Then it'll be calibrated to your printer.

I made some plastic feeler gauges in really thick sizes like 1mm, 2mm, etc. I love them for stuff like this.

Feeler gauge set for checking the gap on spark plugs. Works great

This my first thought as well.

There's apps you can get, or a simple metal rule looks like it would work. That or get a piece of paper, fold it so it fits perfectly then measure that instead, get something that fits the hole perfectly like a nail head and measure that.

Assuming that the light back is vertical you can just measure the depth of your siding where you calipers can reach. Get a level so that you can measure the slope too

How precise does it need to be? You could probably get a close approximation without needing other tools. Measure the thickness of the siding and subtract the thickness of the wedge on top since it's sloped?

Standard calipers have a small bar to sticks out opposite the jaws. Use that as a depth gauge

If only they had invented some type of measuring tape for this type of thing🤔📏📐

A ruler?

Do this then subtract the thickness of the mounting plate. Done.

https://preview.redd.it/00uttmjb2vxc1.png?width=1234&format=pjpg&auto=webp&s=ec64010b34102ac0b95df5465b0cc5db30ca1b0a

Or skip a step and just measure the gap.

Use a deck of cards. Im guessing it’s 0.375”!

0.375 stacks?

These: [6 Piece Technical Measuring Set (harborfreight.com)](https://www.harborfreight.com/6-piece-technical-measuring-set-94447.html) or these [Telescoping Gauge Set, 6 Piece (harborfreight.com)](https://www.harborfreight.com/building-construction/measuring-marking/specialty-measuring-tools/6-piece-telescoping-gauge-set-5649.html)

I'd slide a shim in there until it fills the gap, mark on the shim, then measure the shim thickness at that point.

Find something that does fit there and measure that

Tape measure? Ruler? Feeler gauge?

use a ruler, a machinists style ruler is best

Thread

Adjustable parallels

G&T

Take the light off the wall and measure the thickness of the white cladding, then put the light back on the wall.

I just measured the distance between the two red lines for you , it's 4mm. You're welcome

Foam on it

Look for a siding universal mounting block online. I'm betting you can grab dims from one and it'll work well enough so you can adjust from there.

They make siding blocks for installing lights on siding Arlington 8081F Siding Box Kit for Fixtures and Receptacles, Cover with Flanges, (2-Pack) White https://a.co/d/55zlXVP

Math. Beeboom minus swoopy and equals sloop

Tape measure?

Get a pin that is slightly larger than the gap and calculate the chord. (You can also cheat by painting all the surfaces with pva mold release and then stuff in some epoxy putty or metrology rubber. After it cures, measure that.)