How wide should a slot be for a press fit?
Draw the slot narrower than the material by exactly one kerf. On a 3 mm sheet with a 0.15 mm kerf, draw 2.85 mm: the beam takes the missing 0.15 mm away and the slot comes out at 3.00 mm, which is a press fit. For a loose fit that still glues well, draw the slot 0.1 mm wider than the sheet instead.
Why it is the kerf and not a guess
A slot is a hole, and a hole comes out larger than drawn by one kerf, because the beam removes half a kerf from each side. Drawing the sheet thickness gives a slot 0.15 mm too wide and a joint that wobbles; taking the kerf off first lands it on the thickness.
Measure the sheet, do not trust the label: 3 mm plywood is routinely 2.7 to 3.2 mm, and that error is ten times your kerf.
Test before the real sheet
Cut a test strip with slots in 0.05 mm steps around your number and push an offcut of the same sheet into each. Keep the tightest one that goes in by hand, without a hammer and without force that splits the ply.
Every product MakerWizard makes ships with that strip alongside the parts, drawn for the material and kerf you set.