You need a spacer that is exactly 11.5 mm tall with a 3.4 mm hole through it. You searched Thingiverse and Printables, and you found a hundred spacers, none of them your size. You tried a "parametric" generator and ended up learning just enough OpenSCAD to hate it. All you wanted was a little plastic tube to hold a circuit board off a case, or to raise an electrical outlet flush with a thick backsplash, or to fill the gap on a bolt that turned out too long.
Here is the good news: a spacer or standoff is about the simplest functional part there is. It is a tube with a hole. Get four numbers right, the inner diameter, the outer diameter, the height, and the screw clearance, and it works every time. This guide gives you those numbers with real values for M2 through M6, tells you when to add threads and when not to, and shows you how to print it so the hole stays round and the part stays strong.
What is the difference between a spacer, a standoff, and a washer?
They are three sizes of the same idea: a part that sets or fills a gap around a fastener. A washer is a thin flat disc that spreads a bolt's load. A spacer is a longer tube that sets a fixed distance between two parts, with a bolt passing straight through. A standoff is a spacer that is usually threaded, or takes a threaded insert, so parts screw onto its ends instead of a single bolt running all the way through.
| Part | Shape | What it does | Typical job | |---|---|---|---| | Washer | Thin disc, 1 to 3 mm | Spreads load, stops a screw head digging in | Under a bolt head on a soft or slotted part | | Spacer | Unthreaded tube | Holds a fixed gap, bolt passes through | Raising a fan off a grille, filling a long bolt | | Standoff | Threaded tube (or takes an insert) | Two parts screw onto each end | Mounting a PCB or panel off a surface |
The design thinking is identical for all three. You are choosing an inner diameter for the fastener, an outer diameter for strength, and a height for the gap. The only real fork is whether the fastener passes through (a clearance hole) or threads in (printed threads or a brass insert), covered further down.
What dimensions define a 3D printed spacer or standoff?
Four numbers define it: the inner diameter (the hole for the fastener), the outer diameter (how much plastic is around that hole), the height (the gap you are setting), and the screw clearance built into the hole. Nail those and the shape draws itself.
| Dimension | What it controls | Rule of thumb | |---|---|---| | Inner diameter (ID) | The fastener passes or threads through here | Screw clearance size (table below) for a through-bolt | | Wall thickness | Strength around the hole | 1.5 to 2.5 mm for a load-bearing standoff | | Outer diameter (OD) | Overall footprint | OD = ID + 2 x wall thickness | | Height | The gap between the two parts | Measure the gap you need; this is your most accurate number |
That third row is the one people miss. You do not pick the outer diameter directly, you pick a wall thickness and let it follow the hole. A standoff with a 3.4 mm hole and a 2 mm wall has an outer diameter of 3.4 + 2 + 2 = 7.4 mm. Want it beefier? Grow the wall to 2.5 mm and the OD becomes 8.4 mm. The hole stays where the screw needs it.
If you have not measured the gap or the screw yet, measure before you model. Our guide to measuring with calipers for 3D printing walks through reading the jaws so your 11.5 mm gap does not become an 11 mm guess.
What clearance hole size should you use for the screw?
For a bolt that passes straight through the spacer, make the hole a little larger than the screw's nominal size so it slides through without binding. FDM printers print holes slightly undersized, so you size a touch generous on purpose. These are good starting diameters for a clean through hole:
| Screw | Nominal size | Through hole to model | |---|---|---| | M2 | 2.0 mm | 2.4 to 2.6 mm | | M2.5 | 2.5 mm | 3.0 to 3.2 mm | | M3 | 3.0 mm | 3.4 to 3.6 mm | | M4 | 4.0 mm | 4.6 to 4.8 mm | | M5 | 5.0 mm | 5.6 to 5.8 mm | | M6 | 6.0 mm | 6.6 to 6.8 mm |
These match the clearance numbers in our full guide to bolt and screw holes in 3D prints, so a standoff and the part it bolts to speak the same language. A clearance hole is forgiving: it has millimeters of slack, so if your first print is a hair tight, open the hole a couple tenths and reprint. Do not overthink it, just do not print it exactly nominal, or the bolt will not pass.
How thick should the wall around the hole be?
Keep the wall around the hole at least 1.5 mm, and go to 2 to 2.5 mm for anything that carries real load. Thinner than about 1.2 mm and the tube gets fragile, splits along its layers under a clamped bolt, and barely gives your perimeters room to lay down cleanly.
A quick way to think about it: your printer lays plastic in roughly 0.4 mm-wide lines, so a 1.2 mm wall is three perimeters and a 2 mm wall is five. More perimeters means the standoff resists a bolt torqued down through it instead of cracking. For the general rule behind this, our guide to how thick 3D printed walls should be covers where thin is fine and where it fails.
One more reason to give the wall room: if you plan to thread the standoff or press a brass insert into it, the wall has to survive the insert pushing outward. That is the next decision.
Should a standoff have printed threads or a clearance hole?
It depends on whether one bolt runs all the way through (use a clearance hole) or two parts screw onto the ends (use threads or a brass insert). Do not print fine machine threads if you can avoid them, small printed threads are weak and fiddly, and a heat-set insert almost always holds better.
| Option | How it works | Best for | Watch out for | |---|---|---|---| | Clearance hole + through bolt | One bolt passes through, nut on the far side | Simple spacing, a stack under one bolt | Needs access to both ends | | Heat-set brass insert | Melt a threaded brass insert into the end | Repeated assembly, strong metal threads | Needs the right pilot hole and enough wall | | Printed threads | Model the thread into the plastic | Coarse threads, light duty, one big fastener | Small metric threads print weak and loose |
For most standoffs that mount a board or panel and get taken apart now and then, a heat-set brass insert in each end is the durable answer. It gives you real metal threads a machine screw bites into. Sizing the pilot hole for the insert (and the boss around it) is its own short skill, covered in our guide to heat-set inserts for 3D printing.
If you genuinely want plastic threads, keep them coarse and chunky. Our guide to designing 3D printed threads shows which thread profiles survive FDM and which just strip.
How do you print a standoff so the hole stays round and it stays strong?
Print it standing upright, axis vertical, so the hole prints as a clean circle with no supports and the height comes out dead accurate. This is the right default for a standoff or spacer that gets clamped between two flat parts, because that load is compression, which runs happily along the layer lines.
A few specifics that make the difference:
- Upright gives the roundest hole and the most accurate height. Printed vertically, the bore is drawn as a real circle on every layer, and the height is just a layer count, which is the single most accurate dimension an FDM printer produces. Ask for 11.5 mm tall and you get very close to 11.5 mm.
- Watch out for side loads. A standoff printed upright is weakest against bending, because a sideways push tries to peel the layers apart. If your standoff cantilevers or takes a side load rather than a straight clamp, thicken the wall, or print it lying on its side and ream the hole afterward, since a horizontal bore prints as a slight oval that sags at the top. The reasons layer direction decides this are in why 3D prints break along layer lines.
- The hole shrinks, the height does not. Because FDM holes come out a little undersized, size the bore generous (use the table above) but trust your height number. This is exactly why the fit is worth putting on a slider: the hole is the dimension most likely to need a small nudge after a test fit.
- Stacking spacers to hit a total. If you need several spacers to add up to a set height, print one, measure it, and adjust the height so the stack lands on target. Small first-layer squish adds up over a stack of six.
How Meshra helps you get a standoff right the first time
Every fix above is a number: a 3.4 mm hole, a 2 mm wall, an 11.5 mm height. The problem with a spacer you download as an STL is that those are exactly the numbers you cannot touch. A mesh is a frozen shell of triangles, so "make it 1 mm taller" or "open the hole two tenths" means finding a different file or rebuilding it in CAD from scratch. That is why you end up with a folder of almost-right spacers.
Meshra works the other way around. You describe the part in plain English, for example "a cylindrical standoff 12mm tall with a 3.4mm hole for an M3 screw and a 2mm wall," and it writes real parametric CAD (CadQuery on the OpenCascade kernel) and builds an exact, editable solid, not a mesh. Every dimension you named becomes a slider: the height, the hole diameter, the wall thickness. For how a sentence turns into geometry, see from a sentence to a printable part.
That is what makes the test-and-fit loop painless. Your first standoff prints, the M3 screw is a touch tight, so you drag the hole slider from 3.4 to 3.6 mm and the same code re-executes with that one number changed. The re-run is deterministic and free on every plan, no AI call, so the fit updates in place while the height and wall stay exactly where you set them. Need a stack of eight identical spacers on one plate? The "Print multiple" export nests a chosen quantity onto a build plate sized to your printer and downloads one combined 3MF. When it fits, export STL or 3MF for your slicer, or STEP if you want to keep editing in other CAD.
Meshra also runs a quick printability check on the loaded part and flags a wall thin enough to be a problem (for example "1 wall may be too thin to print reliably, estimate only") before you waste a print on a standoff that would split under a torqued bolt. It is a heads-up on the geometry, not a fit guarantee, so the screw fit still gets confirmed on a real print, but it catches the thin-wall mistake before it costs you a spool of filament.
Frequently asked questions
What is the difference between a spacer and a standoff? A spacer is an unthreaded tube that sets a gap, with a single bolt passing straight through it. A standoff usually has threads (printed, or from a pressed-in brass insert) so two parts screw onto its ends instead of one bolt running through. The body of both is the same tube; the difference is only how the fastener engages.
What size hole do I need for an M3 screw in a spacer? For a through hole where the M3 screw passes freely, model the hole at 3.4 to 3.6 mm. FDM printers print holes slightly undersized, so a nominal 3.0 mm hole would come out too tight. If you want the screw to thread into the standoff instead, use a heat-set insert with its own pilot-hole size, not a plain hole.
How strong is a 3D printed standoff? Strong enough for most mounting jobs if you keep the wall at 2 to 2.5 mm and print it upright, where a clamped bolt loads it in compression along the layers. It is weakest against sideways bending, which pries the layers apart, so for a standoff that takes a side load, thicken the wall or print it lying down and ream the hole. PETG survives repeated assembly and heat better than PLA.
Can I 3D print a spacer to an exact height? Yes, and height is the easiest dimension to hit. Printed upright, a spacer's height is just a stack of layers, which is the most accurate thing an FDM printer does, so an 11.5 mm target comes out very close. The hole diameter is the number that drifts, since holes shrink a little, so size the bore generous and leave height alone.
Do I need supports to print a standoff? No. Printed upright with the hole running vertically, a standoff or spacer needs no supports at all, the walls rise straight and the bore is self-supporting. This is another reason upright is the default orientation for these parts.
Where to start
A standoff or spacer that fits is really just four numbers: the hole sized to your screw, a 2 mm wall, the outer diameter that follows from those, and the height set to your gap. Model the hole a little generous, print it upright, and if the screw is tight, open the hole two tenths of a millimeter instead of hunting for a new file.
In the Meshra builder, describe your standoff with the height, hole size, and wall thickness called out, then tune the fit with a slider after your first test print. The template gallery has maker parts you can derive and edit right now, and pricing covers what each plan includes. Get the hole to a slider and a spacer stops being a folder full of almost-right STLs and becomes a thirty-second fix.
