I recently took on a job building a deck as a favor for a friend. I needed a spacer to create consistent spacing when laying the decks down. In short, I don't like the ones you can pick up at home depot or lowes.
I wanted a spacer that could be pushed, pulled, manipulated, kicked, stepped on, and hammered into place when needed. Because we know that boards aren't always straight.
I printed a bunch of these already and have used them with a lot of success. I can squeeze them with the boards, press them into place, and pull them out without breaking them. I also tested them with the resin printer and it didn't work as well as it should have.
They won't be machine accurate, they will be as accurate to your printer with a +/- deviation equal to the Z height and Step calibration. You can use your own calipers to see what kind of deviation you have. But using them consistently will yield consistent results.

Deck Spacers
6mm = 1/4 inch.
4.5mm = 3/16 inch.
3mm = 1/8 inch.

Drawer Spacers
3mm = 1/8 inch.
2.5mm = 3/32 inch.
2mm = 5/64 inch.
1.5mm = 1/16 inch