The plastic foot on your chair leg cracked, went missing, and now a bare metal tube is gouging a line across the floor every time somebody scoots the chair back. Or the end cap popped off a table leg, a bed frame, a shelf bracket, a trampoline pole, and the ones at the hardware store are all a size too big or a size too small. This is one of the most common broken-part problems there is, and it is almost never worth a trip to the store, because a 3D printer makes a better cap in half an hour for a few cents of filament.
The catch is the same one that trips people up with any replacement part: the fit. An end cap that is a hair too loose walks off the leg within a week. One that is a hair too tight either won't seat or splits as you hammer it on. This guide covers the two cap styles, how to measure a leg so the fit is right the first time, the clearances that make a cap grip, which material to print, and the annoying square-tube case that no round cap will ever solve.
What is a 3D printed end cap and when do you need one?
An end cap is a small cup or plug that closes off the open end of a tube or leg. On furniture it does three jobs: it protects the floor from a sharp metal edge, it keeps dirt and moisture out of a hollow tube, and it stops the leg from scratching or wobbling. You need one whenever the original cap has cracked, worn through, or gone missing, and the replacement you can buy does not match your exact tube size.
That last part is the whole reason to print your own. Furniture and tubing come in a scatter of sizes that were never standardized: 19 mm, 22 mm, 25 mm round; 20 mm, 25 mm, 38 mm square; and every odd metric and inch size in between. A store cap is molded for one exact dimension, so "close" means it falls off. A printed cap is sized to the number your calipers read, which is the only number that matters.
Cap or plug: which end cap style should you print?
There are two ways to close off a tube, and picking the right one before you measure saves you a reprint.
A cap slips over the outside of the leg, like a sock over a foot. Its inner cavity is slightly larger than the leg's outside dimension, and it grips by friction on the outer walls. This is the right choice for solid legs, for legs where you want a visible foot that protects the floor, and for anything where you can't rely on a clean hollow inside.
A plug pushes down inside a hollow tube, like a cork in a bottle. Its outer body is slightly smaller than the tube's inside dimension, and it grips the inner walls, usually with flexible fins or barbs. This is the right choice for thin-wall hollow tubing where you want the cap flush or nearly flush with the end, and where the inside is clean and consistent.
| | Cap (slips over) | Plug (pushes in) | |---|---|---| | Grips on | Outside of the leg | Inside of the tube | | Best for | Solid legs, floor-protecting feet | Hollow thin-wall tube | | Key measurement | Outside dimension of the leg | Inside dimension of the tube | | Grip trick | Internal ribs, or a stretch fit in TPU | Flexible fins or barbs | | Look | A visible foot around the leg | Flush or nearly flush |
If you are not sure, a cap is the more forgiving default: it does not care whether the inside of the tube is rough, painted, or full of a weld seam, because it grips the clean outer face.
How do you measure a tube or chair leg for an end cap?
Measure the bare leg with calipers, not a tape measure. End caps live or die on tenths of a millimeter, and a tape cannot see them. Which number you need depends on the style: for a cap that slips over, measure the leg's outside dimension; for a plug that pushes in, measure the tube's inside dimension.
For a round leg, measure the diameter across the widest point, then rotate the leg a quarter turn and measure again, because tubes are rarely perfectly round. Use the larger of the two honest readings.
For a square leg, this is where people go wrong. Measure the flat-to-flat width across one face, then measure the other pair of faces too, because "square" tube is often a little rectangular. Just as important, look at the corners: extruded square tube has rounded corners with a radius, not sharp 90-degree corners, so a cap with truly square internal corners will bind on the leg before it seats. You want the cap's inner corners to have a matching or slightly larger radius, which a parametric model handles cleanly.
Also measure the wall thickness of the tube if you are printing a plug, and the depth you want the cap to cover. Write every number down. If you are new to reading calipers on tube, our guide to measuring with calipers for 3D printing walks through the tenth-of-a-millimeter mistakes that turn a snug cap into a loose one.
What clearance makes a 3D printed end cap grip?
Clearance is the small gap between the cap and the leg, and it is the single number that decides whether the cap grips or rattles. FDM printers lay plastic slightly wide on inside surfaces, so a cavity modeled at the exact leg size prints too tight. You compensate by adding a deliberate gap, and the size of that gap depends on the material and the fit you want.
| Fit you want | Rigid cap (PLA/PETG), gap per side | Stretch cap (TPU), sizing | |---|---|---| | Snug press fit | 0.15 to 0.25 mm larger than the leg | Model 0.3 to 0.5 mm smaller (interference) | | Firm, still removable | 0.25 to 0.35 mm larger | Model 0.2 to 0.3 mm smaller | | Loose slip fit | 0.4 mm or more larger | Not the point of TPU, skip |
For a rigid cap, the trick that makes a press fit forgiving is internal grip ribs: a few small vertical bumps on the inner wall, maybe 0.4 to 0.6 mm tall. The cap slides on easily, and the ribs deform just enough to bite and hold, so you get grip without needing the whole cavity sized to a perfect tenth. It also means one printed cap can grip a small range of leg sizes instead of exactly one.
For a TPU stretch cap, you go the other way and model the cavity slightly smaller than the leg, so the flexible plastic stretches over it and clamps down. This is why TPU chair-leg caps grip so well and protect floors so quietly, and why they are the go-to for a foot that takes real abuse. For the fine points of press fits and why the same gap behaves differently on a hole than on a peg, see our guide to 3D printing tolerances.
Should you print end caps in PLA, PETG, or TPU?
The right material depends on whether the cap touches the floor, takes impact, or sits outdoors.
| Material | Best for | Watch out for | |---|---|---| | PLA | Indoor caps that don't take abuse, quick tests | Brittle, cracks on hard press fits, softens in a hot car or sunny window | | PETG | Legs that take real force, mild outdoor use | Slightly springier fit, dial clearance a touch tighter | | TPU | Floor-contact feet, quiet grip, impact | Prints slower, needs a stretch-fit sizing, not a rigid press |
For a chair or table foot that scrapes a floor all day, TPU is the honest best answer: it grips by stretch, cushions the contact, and does not crack when someone drags the chair. For a structural cap that has to stay rigid, like the end of a shelf bracket or a bed rail, PETG is the workhorse. Save PLA for indoor caps that live an easy life or for printing a quick test cap before you commit. If you want the full material breakdown, our PLA vs PETG vs ABS guide for functional prints covers where each one earns its place.
How do you design a square tube end cap without CAD?
Square tube is the case that sends people to the forums, because no round cap will ever fit a square leg, and the store rarely stocks the exact square size. The design itself is simple once you have the numbers: a closed square cup, walls thick enough to hold, matching rounded internal corners, and a few grip ribs.
The part you do not want to model by hand is the fit, because the fit is exactly what you need to adjust after the first test print. This is where describing the part in plain language beats drawing it. In the Meshra builder, you write a sentence like "a push-on end cap for a 25 mm square tube with 1.5 mm walls, 20 mm deep, four internal grip ribs," and you get back a real parametric part with a slider for every dimension: the tube size, the wall thickness, the depth, and most importantly the clearance.
That clearance slider is the difference between guessing and dialing it in. You print one cap, test it on the leg, and if it is a touch loose you nudge the clearance down and re-export. Adjusting a slider re-runs the same geometry instantly with no new AI call, so it is free on every plan and takes seconds, not a fresh design. Meshra also flags thin walls before you print and gives you a rough filament weight so you know a cap costs pennies, and it exports STL for your slicer, 3MF for OrcaSlicer or Bambu Studio or PrusaSlicer, and STEP if you want the CAD file too.
How do you print an end cap so it fits and holds?
Orientation is the one printing choice that matters. Print the cap open side down, so the flat closed face is on top and the open mouth sits on the bed. This puts the layer lines running around the walls, which is exactly the direction that resists a cap being pushed on and pulled off, and it means the walls print with no supports inside the cavity. Supports inside a small cap are a nightmare to remove and leave a rough surface that fights the fit.
A few more practical settings:
- Walls: 3 or 4 perimeters (roughly 1.2 to 1.6 mm) so the cap grips without splitting. A single-perimeter cap cracks the first time you press it.
- Infill: it barely matters on a part this small, 15 to 20 percent is plenty.
- First layer: the closed top prints as a clean flat surface, so it looks good facing up as the visible foot.
- Test first: print one cap, test the fit, adjust the clearance slider, then print the set of four. A test cap costs a few cents and saves you printing four caps that all fall off.
Frequently asked questions
What size cap fits a standard chair leg? There is no single standard. Common metal chair legs run 19 mm, 22 mm, or 25 mm round, and kitchen and folding chairs are often 20 mm or 25 mm square. The only reliable move is to measure your own leg with calipers, because a store cap molded for 22 mm will not stay on a 20 mm leg.
How much clearance should a 3D printed end cap have? For a rigid PLA or PETG cap that slips over the leg, model the internal cavity about 0.2 to 0.3 mm larger than the leg per side, and add small internal ribs for grip. For a TPU stretch cap, model the cavity 0.3 to 0.5 mm smaller than the leg so the flexible plastic clamps down.
Should I print chair leg caps in TPU or PLA? TPU for anything that touches the floor: it grips by stretch, cushions the contact, and does not crack when the chair gets dragged. PLA is fine for a quick indoor test cap or a foot that lives an easy life, but it can crack on a hard press fit and softens in heat.
How do I make a square tube end cap when round ones do not fit? Model a square cup sized to your measured flat-to-flat width, with internal corners that have a matching rounded radius, since extruded square tube has rounded corners. Describe it in Meshra with those numbers and tune the clearance slider after a test print, rather than trying to scale a round cap that will never seat on a square leg.
Why does my printed end cap keep falling off? The fit is too loose, or the walls are too smooth to grip. Nudge the clearance tighter by 0.1 to 0.2 mm, add a few internal grip ribs so there is something to bite, or reprint in TPU for a stretch fit that clamps down instead of relying on a perfect press.
Where to start
Pop the broken cap off, measure the leg with calipers (outside dimension for a cap that slips over, inside dimension for a plug that pushes in, and both pairs of faces on a square tube), and note whether it is round or square. Then, in the Meshra builder, describe the cap with those numbers in the sentence and you get a parametric part with a slider for the clearance, so the fit is something you tune in seconds, not something you guess and reprint. Browse the template gallery for shapes to start from, or see pricing for the plans. Your first part is free, no card required, so you can measure a leg and print a cap that stays on in one sitting.
An end cap is the small satisfying kind of print that quietly fixes something you walk past every day. Measure honestly, give the fit a slider you can nudge, print it open-side-down in a material that suits where the cap lives, and that chair stops gouging your floor for good.
