Custom 3D printed replacement parts can bring back a broken knob, clip, bracket or cover when the maker no longer sells a spare. Getting one that fits comes down to good measurements and the right material. This guide shows how to measure a part, what to send us and how to order a replacement.
What makes a good printed replacement
Many small plastic parts around the home can be reproduced as an FDM print. Good candidates include:
- knobs and dials for appliances, furniture and equipment
- clips, latches and brackets
- battery covers and access panels
- feet, bumpers and end caps
- shelf supports, drawer stops and cable guides
- spacers and washers for light loads
Some parts aren't a good fit. We'd steer you away from printing anything where a failure could hurt someone, such as parts for brakes, child seats, ladders or anything holding a heavy load overhead. Parts that get very hot, like anything inside an oven or near an engine, are beyond what our filament prints are made for. And we don't print weapon parts at all.
How to measure the part
A pair of digital calipers is the best tool for the job. They're inexpensive and far more precise than a ruler. Measure in millimeters if you can, since 3D printing software works in millimeters.
- Measure the overall size first: length, width and height.
- Measure every feature that has to fit something: hole diameters, shaft sizes, slot widths, wall thickness and the distance between mounting holes, center to center.
- Measure the mating part too. If a knob fits onto a shaft, measure the shaft, not just the hole in the old knob. A worn or cracked original may no longer be the right size.
- Measure more than once. Take each important reading two or three times and write down the one you trust.
- Note shapes that aren't obvious, like a D-shaped shaft, a tapered peg or a snap-fit hook.
If the original is broken into pieces, keep them together and measure what you can. Even a partial part tells the designer a lot.
Photos and sketches that help
Good photos save design time. Take them in daylight or bright, even light, and include:
- the part from the front, side and top, next to a ruler or with the calipers in the shot
- close-ups of clips, threads or unusual features
- the spot where the part goes, so we can see how it fits
A quick sketch with your measurements written on it is often the single most useful thing you can send. Photos (JPG, PNG or HEIC) and drawings (PDF) all upload through the request form. Our post on turning a sketch into a 3D print shows how to draw one we can model from.
Tolerances: why an exact copy might not fit
FDM prints are accurate, but not perfect to the hundredth of a millimeter, and parts that fit together need a small gap. As a starting point, designers often allow roughly 0.05–0.15 mm per side for a tight press fit and about 0.2–0.3 mm per side for something that should slide or turn freely. The right value depends on the material and the part.
Round holes also tend to print slightly smaller than modeled, so a hole meant for a bolt is usually drawn a little oversize. Tell us exactly what the part has to fit, such as "slides onto a 6 mm D-shaft" or "snaps into a 20 mm square opening", and we'll allow for it in the design.
If you already have a 3D model of the part, our guide on preparing your 3D model before ordering covers units, scale and wall thickness.
Choosing the material
| Material | Good for | Watch out for |
|---|---|---|
| PLA / PLA+ | indoor knobs, covers, brackets and organizers | softens at about 55–65 °C (130–150 °F), so not for hot cars or sunny windowsills |
| PETG | parts that see more heat, sun, moisture or slight flexing | quoted separately; a little less rigid than PLA |
| TPU | feet, bumpers, gaskets, grips and anything that must flex | quoted separately; too flexible for rigid parts |
PLA and PLA+ are included in our starting prices. Our guide to PLA vs PETG vs TPU for custom parts goes deeper. Here in Arizona, a car parked in the sun can get hot enough to soften PLA (an Arizona State University study measured dashboards at 157 °F), so for anything that lives in a vehicle, PETG is the better choice of the two.
Ordering and pricing
Most replacement parts fall into our Small tier: up to 4 in (100 mm) on the longest side, from $25 plus $9.99 US shipping, made in 3–5 business days. If we need to model the part from your measurements, design time is $40 per hour with a 1-hour minimum, quoted before we start. Every order gets a written quote first, within 1–2 business days.
Need several? Bulk pricing starts at 10 pieces with 10% off. If fit is critical, you might order one part first, test it, then order the rest. Full pricing and the request form are on our custom 3D printing page.
Replacement Parts FAQ
Can you copy a part from photos alone?
Sometimes, for simple shapes. Photos with a ruler in the shot help, but measurements of the features that must fit are what make a replacement work. A sketch with dimensions plus photos is the best combination.
Is a 3D printed part as strong as the original?
It depends on the part. For light household jobs, a well-designed printed part is often strong enough, especially with extra walls and a good print orientation. Printed parts aren't suitable where a failure could cause injury.
What if I don't know what the original is made of?
You don't need to. Tell us what the part does, where it lives and whether it gets hot, wet or flexed, and we'll recommend PLA, PETG or TPU in your quote.
Got a broken part and no spare in sight? Measure it, snap a few photos and send them over. We'll tell you what it will take to replace it.