No calipers. No ruler. Print the ArUco marker sheet and capture mat, photograph your part, and get real millimeter dimensions. Pair with the free printable gauges below for hands-on measurements without any bought tools.
Six DICT_4X4_50 markers (IDs 0–5) at 30 mm each, with dual cut guides: quiet-zone dashed for gluing into a photo-booth corner, marker-edge solid for standalone use on a flat surface.
A flat measurement stage with all six ArUco markers at precisely known positions. Lay a part on it, photograph it, and the rectifier converts pixels to millimeters. Includes an ISO/IEC 7810 ID-1 card outline (85.60 × 53.98 mm) as a built-in scale check — if your bank card matches the outline, the mat is true.
Download the mat or marker sheet PDF. Print at exactly 100% scale — most printers default to 'fit to page' which rescales. Confirm in your print dialog that no scaling is applied.
Lay any bank card on the printed ID-1 outline. If the card matches the rectangle exactly, the mat is true. If not, measure the 140 mm reference bar on the mat and enter that reading when uploading.
Place the part on the mat. Take one overhead photo. Upload to PrintMakerAI — the ArUco rectifier removes perspective and converts pixel distances to real millimeters automatically.
Four printable gauges that cover the measurements you need for 3D-printed replacement parts. Free STL downloads — PLA, 0.2 mm layers, no supports.
3–18 mm hole diameter
Push tip-first into a hole. The last step that enters without forcing is the diameter.
Download STL2–20 mm pocket or hole depth
Rest the bar flush on the surrounding surface. The deepest finger that bottoms out is the depth.
Download STL1.0–6.0 mm walls and plates
Slide the wall into slots from largest to smallest. The tightest slot it enters is the thickness.
Download STLR1–R8 mm outside corners
Press notches against an outside corner. The notch that sits flush with no gap or rock is the radius.
Download STLArUco is an open, well-documented fiducial system used in computer vision and robotics. The dictionary format (DICT_4X4_50) encodes marker IDs in a 4×4 bit grid — small enough to print at 30 mm and reliably detect even in a low-resolution phone photo. The six-marker layout provides redundancy: the rectifier can solve the homography matrix from as few as four visible corners.
Camera perspective can be corrected mathematically, but uniform scaling cannot — if your printer printed the page at 95%, every measurement would be off by 5% with no way to detect it. The ISO/IEC 7810 ID-1 standard fixes card dimensions at exactly 85.60 × 53.98 mm worldwide. Laying your bank card on the outline is a one-second check that catches any print-scale error before it corrupts your measurements.
The rectifier is built into PrintMakerAI — upload a photo taken on the mat and it undoes the perspective automatically. The marker sheet and mat are also compatible with any OpenCV-based ArUco pipeline if you prefer to roll your own.
PLA is ideal — stiff and dimensionally stable. Print flat as oriented, 0.2 mm layers, 3+ perimeters, 40%+ infill, no supports, 100% scale. The thickness comb has a slot_compensation parameter (default 0.15 mm) — calibrate it once with a part of known size and reuse it forever.
Step gauges read in fixed increments (1 mm for bores, 2 mm for depths, 0.5 mm for thickness), so you're choosing between labeled values rather than reading a continuous scale. A calibrated FDM printer resolves those steps reliably. They won't replace calipers for ±0.05 mm work, but for 'what size is this hole so I can design a part that fits' they're more than enough.
Once you have real dimensions, PrintMakerAI can design the part from a description — replacement brackets, custom enclosures, fitted mounts — on the same geometry engine that generated these tools.
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