Gridfinity: the 42 mm grid built to fit

You download a Gridfinity bin, print it as-is and drop it onto the baseplate. Either it won't go in — you force it, and it goes in with the crack of stressed plastic — or it rattles around in its pocket with room to spare. The standard is defined down to a tenth of a millimetre: the foot, the socket and the gap between them are fixed dimensions that thousands of parts share. The problem isn't the design, which fits perfectly on screen; it's that FDM shifts those dimensions before the part reaches your hand, and always in the same direction. This article is the map of those dimensions, and of how much you have to correct them so your bin drops into any baseplate.

The grid: 42 mm pitch, 7 mm unit

Gridfinity rests on two numbers. The first is the grid pitch: 42 mm. Each cell occupies a 42 × 42 mm square, and every part in the system — bins, baseplates, adapters — is measured in whole multiples of that cell. A "2 × 1" bin covers two cells wide by one deep; a "3 × 2" baseplate offers six pockets. The 42 isn't arbitrary: it has plenty of divisors and leaves a cell that comfortably houses the feet with their chamfers without wasting space.

The second number governs height: the 7 mm unit, abbreviated U. A bin's height is counted in U, and here's the detail that trips people up most: the figure in U is the height of the body, without the stacking lip. The lip adds on top, roughly 4.4 mm, so a 3U bin is 21 mm of body and, with the lip, stands around 25.4 mm tall. That lip doesn't count towards the pitch of a stack: when you stack, the foot of the upper bin sinks into the lip of the one below and recovers those 4.4 mm, so each bin in the stack rises by exactly 7 · U. Model the body in multiples of 7 mm and let the lip sit above it; that's where the next foot nests.

The foot: three stacked bands and a chamfer that centres the part

What makes Gridfinity Gridfinity is the foot profile, identical across every part that sits on the baseplate. Look at it in section and you'll see three stacked bands, from the bottom up: a 0.8 mm lower chamfer that flares the mouth of the foot, a 1.8 mm straight wall in the middle and a 2.15 mm upper chamfer that closes against the body. They add up to a 4.75 mm foot height. The top face of that foot measures 41.5 mm on a side: the 42 mm of the cell minus 0.25 mm of clearance on each side.

The 45° lower chamfer isn't decorative. When you drop the bin onto the baseplate slightly misaligned, that inclined plane meets the corner of the socket first and slides the part towards the centre as it descends: it self-centres. That's why it matters so much that this chamfer comes out clean. It's the guiding geometry, and any distortion at its mouth ruins the fit.

The 0.25 mm of clearance per side is the key to the whole fit — and it's also where FDM betrays you.

Why 0.25 mm of clearance isn't your clearance

The standard leaves 0.25 mm of gap per side between the foot face (41.5 mm) and the socket wall. On paper that's a generous locating gap: the part drops, centres and sits firm without rattling. Print it at nominal size, however, and the gap disappears.

The reason is FDM's systematic bias, the same one Real printed clearances works through: sockets shrink and feet grow. The baseplate socket is a hole, and holes come out small — the bead bites inwards and the material contracts as it cools. The foot is a protrusion, and protrusions come out fat — the bead is laid down outwards, and the first layer squashes and spreads. Both errors push the same way: they eat the gap. A well-calibrated foot and socket easily swallow 0.10–0.15 mm per side, and out of a budget of 0.25, you're left with a bare tenth: a rub, if not outright interference.

That's why you shouldn't print to the standard's clearance: raise it for your printer. A good Gridfinity generator exposes clearance as an editable parameter (0 to 0.5 mm per side in the standard). Let the nominal 0.25 land at a real 0.15 and, if your feet come out fatter than they should, push up to 0.35–0.40 mm/side until the bin drops in with a little play and centres itself. It's exactly the reasoning of Choosing the fit: clearance, transition, interference: you pick the family — here, guided locating — and then turn the intent into a number measured on your machine, not copied off the drawing.

Baseplates: lite, magnetic and screw-down

The baseplate is the plate that receives the feet. Its top face is a grid of sockets, one per cell, each with the negative of the foot profile plus the clearance. There are three families, depending on what they carry underneath.

The lite is just sockets over a thin floor: the lightest and quickest to print, with no fixing — it stays put by its own weight and the friction of the feet. The magnetic thickens the floor to about 2.8 mm to house a 6 × 2 mm magnet in a pocket under each cell, leaving a closed ceiling of ~0.8 mm above it (a couple of solid perimeters) that you glue the magnet against. That ceiling does two jobs: it gives a gluing surface and it hides the magnet from above. The screw-down swaps the magnet pocket for an M3 through-hole to fix the plate to a surface.

Magnets and screws sit on the same grid: four per cell, 13 mm from the cell centre towards each corner. That position guarantees that a magnetic bin of any size finds a magnet under every one of its feet.

The stacking lip and the parametric bins

Bins stack thanks to the stacking lip: the top 4.4 mm of the wall carry a profiled rim that is, in fact, the negative of the baseplate socket. When you put one bin on top of another, the foot of the upper one nests inside that lip and centres on the same 45° chamfers that would seat it in a baseplate. The foot sinks into the lip and recovers its height — which is why the figure in U is counted without it — and the stack sits stably and aligned without touching the contents of the lower bin. Compress that lip or model it thinner and the foot no longer seats cleanly, and the stack wobbles.

The rest of the bin is parametric and controlled with a handful of dimensions. The height, given in U. The internal dividers: vertical slots cut every 21 mm — half a cell — at 1.6 mm wide to house a 1.2 mm divider with its own sliding clearance. The label tabs: a small front ledge where the printed or written label goes. The scoops: a curved inner ramp at the bottom that lets you sweep small parts up with a finger instead of scraping at a square corner.

The sliding divider and the lid are separate parts of the same system. The divider drops into those 1.6 mm slots; the lid mounts over the lip and closes the bin so you can move it without spilling what's inside.

Adapters, connectors and printing for compatibility

Two loose bins on a lite baseplate drift apart when you slam the drawer shut. The community pattern for locking them is the edge connector: a dovetail pocket cut under the plate that takes a bow-tie clip which grips two adjacent plates and locks them against separation. There's no official connector standard with published dimensions: it's a community convention, and each generator draws its dovetail with slightly different measurements. So, with a connector, print the clip and its socket with the same generator and the same clearance; don't mix a clip from one project with a plate from another and expect the dovetails to line up. The same family covers the adapters that carry the grid into a specific drawer or a Kallax cubby: they're bespoke plates with the same socket profile on top.

When printing, orient the bin feet-down, the way it's used. The foot chamfer is at 45°, self-supporting (above the overhang threshold) and needs no supports. But that same orientation puts the mouth of the foot on the first layer, and the first layer squashes: elephant's foot fattens exactly the band that fits and closes the gap from below. It's the effect Holes, pegs and first-layer squish describes, and here it acts on the most sensitive fit geometry there is. Compensate for it with clearance and with the slicer's elephant's-foot compensation, never by touching the chamfer angle, which is what carries the part to the centre. And don't compensate twice: if you enable the slicer's XY compensation, don't also open the clearance in the model.

Calibrate the clearance once

The foot profile, the 42 mm pitch and the 7 mm unit are fixed by the standard; the one number that's yours to set is the clearance. The size in grid units (1 × 1, 2 × 1, 2 × 2, 3 × 2 and so on) and the height in U are just how big and how tall you want the part. Set the clearance once with the strip above, and every bin you print from then on — body, divider or lid — drops into any compatible baseplate in the world.

When you want the parts locked to each other rather than merely resting — no magnets, no screws, pure click geometry — the next step is Clickfinity: bins that snap into place.