A plywood divider should slide into its slot without a wrestling match. Yet a slot laid out from the thickness printed on a sheet can turn out too tight or too loose. That label is a useful starting point, not a substitute for checking the piece on the bench.
Keep a small, clearly marked offcut from the sheet you plan to use. Measure its thickness at a few places with calipers if you have them, and check the actual divider too. Sanding and manufacturing variation can leave plywood a little different from its nominal size; an offcut from another sheet may not tell the same story.
Before working on the box, make a trial slot in scrap using the same method intended for the finished part. Secure the scrap and follow the safety guidance for your tools. Try the sample in that slot, keeping its faces square to the opening rather than rocking it in to force a fit.
For a removable divider, aim for a smooth hand fit: it should slide in and lift out without hammering, while staying upright rather than rattling about. Check the fit along the whole slot. A tight spot at one end may be a tapered slot or a rough patch, not a reason to thin the entire divider.
For a glued divider, follow the adhesive maker’s joint-fit guidance instead of making the slot deliberately loose to hold more glue. If the parts will be finished before assembly, test the planned finish on the sample and let it dry as directed before checking the fit again. Keep intended glue surfaces free of finish unless the adhesive instructions allow otherwise.
Practical takeaway: label one offcut with the sheet it came from and use it to prove the slot before cutting the full batch. A short scrap test is cheaper than a box full of dividers that need persuading.
PlywoodBox DividersShop Tips