For holding 21 (6 + 15) Metric sizes and 23 (6 + 17) SAE sizes. Created specifically to hold the "complete" SAE & metric thread checker set from the "necklace" here: https://www.amazon.com/dp/B06ZYD4SS8/ Though hopefully it also fits the pretty red and blue sets.

I used this to generate the base with "Gridfinity Refined" side-magnets: https://gridfinity.perplexinglabs.com/ If you're not happy with this particular base, no problem: use any solid base and add the "holes" STL files as negative parts to your slicer. They should already have the correct Z-offset to go perfectly in-position.

If my provided tolerances are too low, or you'd like to make changes, here are the CAD links: Metric 1x3 https://cad.onshape.com/documents/78771f65f49195f429907fc8/w/8c2d6bd2569ff98dc5a3e3d4/e/79526cd395f31b3a9e6060fd SAE 1x3 https://cad.onshape.com/documents/ec9f0e612a71a7711682e265/w/77e90185675c48a1df955d6c/e/941683c5eb2a559fb1ab552e Metric & SAE 1x4 https://cad.onshape.com/documents/6c50033bde1b11062b0f7e0f/w/83f966eaef179ab18af43010/e/4362b0f36c0cce8e833286d4 I did my best to maximize clearance between the holders and edges.

My first upload, so hopefully I did it right. 🤷