You want a bearing to sit in a printed part and just work: press it in, it stays put, the shaft spins free. Instead you get one of two annoying failures. Either the seat is too big and the bearing rattles loose or falls out the first time you flip the part over, or the seat is too small and you're leaning your whole body weight on a bearing that will not go in, cracking the plastic around it. Sometimes both on the same print, because you guessed the pocket at a round 22 mm.
Bearings are one of the highest-value things you can 3D print around, spinners, lazy susans, wheels, motor mounts, filament spool holders, camera rigs. And the fit is almost entirely about one number: the diameter of the pocket the bearing sits in. Get that right and everything downstream is easy. This guide covers the real dimensions of the common bearings, exactly how much clearance to leave for a press fit, how to design a seat that holds the bearing at the right depth, and which way to print it so the hole comes out round.
What are the dimensions of a 608 bearing (and the other common ones)?
A 608 bearing is 8 mm bore, 22 mm outer diameter, 7 mm wide, written 8 x 22 x 7 mm. It is the skateboard bearing, the most common one in the maker world, so if a design just says "a bearing" it usually means a 608. The other bearings you'll run into follow the same naming logic, and their sizes are fixed standards, not something that varies by brand.
| Bearing | Bore | Outer diameter | Width | |---|---|---|---| | 623 | 3 mm | 10 mm | 4 mm | | 625 | 5 mm | 16 mm | 5 mm | | 626 | 6 mm | 19 mm | 6 mm | | 688 | 8 mm | 16 mm | 5 mm | | 608 | 8 mm | 22 mm | 7 mm | | 6000 | 10 mm | 26 mm | 8 mm |
The outer diameter is the number that sets your pocket size. The width sets how deep the seat should be. The bore is the shaft size, which matters for what spins inside, not for how the bearing mounts. Measure your actual bearing with calipers before you design anything: bearings are made to tight tolerances so the standard numbers are reliable, but it takes ten seconds to confirm and it saves a reprint. If you're new to reading a caliper, our guide to measuring with calipers for 3D printing walks through it.
How much clearance should a 3D printed bearing seat have?
For a press fit that holds without cracking the plastic, model the pocket about 0.1 to 0.2 mm smaller than the bearing's outer diameter total, so roughly 0.05 to 0.10 mm of interference on each side. For a 608 (22 mm outer diameter) that means a pocket of 21.8 to 21.9 mm. The bearing goes in with firm thumb pressure or a light tap, and the plastic grips the outer race all the way around.
That interference number is small on purpose. FDM plastic does not compress much before it splits, so a pocket 0.5 mm undersize will not "squeeze in," it will just wedge and crack a thin wall. Start on the loose end of the range and tighten only if the bearing spins in the seat.
Two things change the number:
- Material. PLA is stiff and brittle, so keep interference light, closer to 0.05 mm per side (a 21.9 mm pocket for a 608). PETG has more give and tolerates a slightly tighter 0.10 mm per side (21.8 mm). ABS and ASA sit in between.
- A heat assist. A steel bearing warmed to around 80 C with a heat gun or a mug of hot water expands enough to drop into a pocket that was stubborn cold, then locks tight as it cools. If you want a really solid press fit, design for the tighter end and use heat to seat it.
If you would rather the bearing drop in easily and be held by a lip or a dab of glue instead of pure friction, that is a slip fit with retention: model the pocket 0.1 to 0.2 mm larger than the outer diameter (22.1 to 22.2 mm for a 608) and give it something to seat against. That is the more forgiving choice for a first print, and it is covered next.
Here is the whole thing as one table, using a 608 as the worked example:
| Fit | Pocket vs. outer diameter | 608 pocket (22 mm OD) | Feel | |---|---|---|---| | Press fit (PLA) | 0.05 mm under per side | 21.9 mm | Firm push or light tap, held by friction | | Press fit (PETG) | 0.10 mm under per side | 21.8 mm | Needs a tap or heat, very solid | | Slip fit with lip or glue | 0.05 to 0.10 mm over per side | 22.1 to 22.2 mm | Drops in, held by a shoulder |
These are starting points, not per-printer gospel. Your printer's real-world dimensional accuracy shifts them, which is exactly why you want the pocket on an adjustable slider (more on that below) so one test print calibrates it. For the general theory behind why holes and pockets need clearance an outside diameter does not, see our 3D printing tolerances guide.
Should the bearing press all the way through, or seat against a lip?
Design a shoulder (a small lip) so the bearing seats to a defined depth instead of pressing straight through the part. Make the pocket as deep as the bearing is wide (7 mm deep for a 608), then add a back wall or a lip with an opening smaller than the bearing's outer diameter but larger than its inner race, so the bearing stops against it and the shaft still passes through freely.
The key detail people miss: the lip must only touch the outer race, never the inner race or the metal shields. A ball bearing works because the inner and outer races rotate independently. If your lip presses on the inner race or pinches the shield, you have just clamped the bearing solid and it will not spin. So size the lip opening to clear the inner race. On a 608, the outer diameter is 22 mm and the bore is 8 mm; a back opening of around 15 to 18 mm catches the bearing's outer edge while clearing the rotating inner race and the shaft, so nothing rubs the spinning parts.
A quick way to think about it:
- Pocket diameter: the bearing's outer diameter, minus your press-fit interference.
- Pocket depth: the bearing's width, so it sits flush (or a hair deeper).
- Back lip opening: bigger than the bore, smaller than the outer diameter, touching only the outer race.
- Wall around the pocket: at least 2 mm, ideally 3 mm, so the press-fit force does not split it. A press fit into a thin wall is the classic way to crack a part. If you want the reasoning on wall counts, see how thick 3D printed walls should be.
Which way should you print a bearing seat so the hole comes out round?
Print the part so the bearing pocket opens upward, with its axis vertical (along Z). A hole or pocket printed this way comes out as a clean stack of circles and holds its diameter best. The catch is that FDM holes almost always print slightly undersize, because the inner wall of a hole gets pulled in a little as each layer cools, so a pocket modeled at exactly 21.9 mm often measures 21.7 or 21.75 mm on the part. That is another 0.1 to 0.2 mm of unplanned interference, which can turn a nice press fit into an uncrackable one.
You have two clean ways to handle it:
- Model the pocket a touch bigger to cancel the shrink, then confirm with a test print.
- Print the pocket opening up and skip a bridged roof, so you can measure and, if needed, chase the hole to size, though for a bearing you rarely need to.
Avoid printing the seat as a horizontal bore lying on its side. That way the hole prints as an oval (the top overhangs and droops), and an oval pocket grips a round bearing on only two points. If your part geometry forces a sideways bore, expect to tune the fit more and lean toward the slip-fit-with-lip approach.
How do you get the shaft to actually spin freely?
Leave clearance on whatever passes through the bore, and never let the printed part touch the bearing's inner race and outer race at the same time. If you are printing your own shaft or pin to run in the bore, size it 0.2 to 0.4 mm under the bore diameter (so about 7.6 to 7.8 mm for a 608's 8 mm bore) so it turns without binding, the same clearance range you would use for any printed pin in a printed hole. If you are using a metal bolt as the shaft, a shoulder bolt or an M8 bolt with a smooth section through the bore works well.
The most common "it won't spin" mistake is a design where the bracket pinches both races. Picture a bearing sandwiched between two printed faces: if both faces touch the full diameter, they clamp the inner and outer races together and the bearing seizes. The fix is the same lip idea as above, contact only the outer race on the mounting side, and only the inner race (or a washer on the shaft) on the rotating side.
How Meshra helps you dial in the bearing fit
This is exactly the kind of part where designing it parametrically beats downloading a fixed STL you cannot easily change. In Meshra you describe the part in plain English and it writes real parametric CAD (CadQuery on the OpenCascade kernel) and builds an exact solid, not a triangle mesh. You can call out the bearing directly: "a bearing block for a 608 bearing, 22 mm outer diameter and 7 mm wide, with a 21.9 mm seat pocket, a retaining lip on the back, and a 3 mm wall around the seat." You get a watertight, millimeter-exact model with a slider for every dimension it generated.
That slider is the point. The one number that decides whether a bearing seat works is the pocket diameter, and it is the one number you cannot perfectly predict before a test print, because it depends on your printer, your material, and hole shrink. So print one, and if the 608 spins in the seat, open the parameter drawer, nudge the seat diameter down by 0.1 mm, and the same code re-executes deterministically with the new number. Every other feature stays exactly where it was, there is no AI call, and it is instant and free on every plan. Calibrating a press fit becomes a two-second drag instead of a remodel.
A couple of Meshra touches help specifically here. Any slider named for a fit, clearance, tolerance, or gap gets a small info badge in the parameter drawer, and Meshra recognizes when a value lines up with common hardware, including a 608 bearing's bore and outer diameter, and says so in plain language as you drag. The printability summary also reads the part the moment it loads and flags a wall too thin to survive a press fit (for example "1 wall may be too thin to print reliably, estimate only"), so you catch a fragile seat wall in the browser instead of after it cracks. Both are fast estimates, not slicer-accurate guarantees, but they catch the two mistakes that ruin bearing mounts most often.
When the fit is right, export STL or 3MF for your slicer, or STEP if you want to open the block in another CAD tool later, all in millimeters and clearly labeled so nothing guesses the wrong unit.
FAQ
What size hole for a 608 bearing press fit?
Model the pocket at 21.8 to 21.9 mm, not 22 mm. A 608 has a 22 mm outer diameter, and you want roughly 0.05 to 0.10 mm of interference per side for a press fit that grips without splitting the plastic. Use 21.9 mm for brittle PLA and 21.8 mm for more forgiving PETG, then adjust after a test print. Remember FDM holes print slightly undersize, so measure the real part.
Why does my printed bearing seat crack when I press the bearing in?
Two usual causes: the pocket is far too small (more than about 0.2 mm undersize, which wedges instead of pressing), or the wall around the pocket is too thin to take the outward force. Keep interference to 0.05 to 0.10 mm per side and the surrounding wall at least 2 to 3 mm thick. Warming the bearing to around 80 C before pressing also helps it seat without stressing the plastic.
Why won't my 3D printed bearing mount spin?
Almost always because the printed part is touching both the inner and outer race at once, clamping the bearing solid. A bearing only spins if the inner and outer races can move independently. Design any lip or face so it contacts only the outer race on the fixed side, and only the inner race (or a washer on the shaft) on the rotating side.
Should I use a press fit or a slip fit with glue?
Press fit if you want a clean, tool-free hold and you are willing to calibrate the pocket with a test print. Slip fit with a retaining lip or a dab of glue if you want it to drop in easily and you would rather not chase the exact interference number. For a first attempt, the slip fit (pocket 0.1 to 0.2 mm larger than the outer diameter, seated against a lip) is the more forgiving choice.
Can I print the bearing itself instead of buying one?
You can print a working print-in-place bearing for light, low-speed jobs (a spinning sign, a toy), and plenty exist on the model sites. But for anything that carries load, spins fast, or needs to last, a real 1 to 2 dollar steel bearing pressed into a printed mount will run smoother and outlast a printed one by a wide margin. Design the mount, buy the bearing.
Where to start
Grab your bearing, measure the outer diameter with calipers, and describe the mount in the Meshra builder with the seat pocket called out about 0.1 mm under that number (for a 608, try a 21.9 mm seat with a 3 mm wall and a retaining lip). Print one, and if the bearing spins in the seat, drag the seat-diameter slider down 0.1 mm and reprint, no remodel. The template gallery has mounts and holders with parameters already exposed if you would rather start from something than a blank prompt. For the clearance math behind every mating part, read the 3D printing tolerances guide; see pricing for current generation allowances, or create an account to keep the part and tune the fit after a test print.
A bearing mount lives or dies on one dimension. Size the pocket a hair under the outer diameter, seat it against a lip that only touches the outer race, print it opening-up, and keep that pocket on a slider so the next print corrects the fit in seconds.
