What is the difference between STL and STEP files?

An STL file describes a model's surface as a mesh of triangles. It records shape but no engineering data — no exact dimensions, units, or feature history — and its accuracy depends on how finely the mesh was exported. A STEP file (.step or .stp) is a precise boundary-representation CAD format that stores exact geometry, curves, and units. STEP is editable and dimensionally accurate; STL is a fixed approximation. For most service-bureau work, STEP is the better file to send, with STL as a widely accepted fallback.

Should I send my 3D printing service an STL or a STEP file?

Send STEP when you have it. STEP gives the provider exact geometry and units, makes accurate quoting easier, and allows minor adjustments like adding draft or thickening a wall. Send STL when STEP isn't available — it's universally accepted and fine for most prototype work, as long as it was exported at sufficient resolution. When in doubt, send both: STEP as the source of truth and STL as a render-ready backup.

What resolution should I export an STL at for 3D printing?

Export with a chord/deviation tolerance around 0.001–0.005 inches (roughly 0.01–0.1 mm) and an angle tolerance near 10–15 degrees. Too coarse and curved surfaces show visible facets; too fine and the file balloons in size with no printable benefit, since most printers can't resolve below their layer height and nozzle width. A few megabytes is typical for a normal part. If your CAD tool offers 'high' or 'fine' export presets, those are usually a safe starting point.

Can a 3D printing service edit an STL file?

Only in limited ways. Because an STL is a fixed mesh with no feature history, providers can repair holes, reorient, scale, or hollow it, but they cannot cleanly change dimensions, add draft, or modify features the way they can with a STEP file. If you expect the provider to make engineering adjustments, send STEP. If the part is final and only needs printing, STL is fine.

What other file formats do 3D printing services accept?

Beyond STL and STEP, most bureaus accept OBJ (mesh with color/texture, common for full-color and artistic prints), 3MF (a modern mesh format that bundles units, color, and print settings and avoids many STL pitfalls), and IGES (an older precise CAD format). Native CAD files like SolidWorks or Fusion are sometimes accepted but less portable. For functional engineering parts, STEP or 3MF give the cleanest results; for visual or full-color models, OBJ is common.

STL vs STEP Files: Which Format to Send Your 3D Printing Service

The file you send a 3D printing service shapes everything downstream — how accurately they can quote, whether they can adjust your part, and how closely the printed result matches your intent. The two formats you'll reach for most are STL and STEP, and they are fundamentally different. This guide explains when to use each and how to prep files that print right the first time.

When you're ready to order, the 3D Prototyping Hub directory lets you submit your file and specs directly to verified providers.

STL: A Mesh of Triangles

An STL file represents your model's surface as thousands of small triangles. It captures the shape of the part but discards the engineering data behind it — no exact dimensions, no units baked in, no feature history. What you see is a frozen approximation, and its quality depends entirely on how finely it was exported.

STL's strengths:

Universal — every printer, slicer, and service bureau accepts it
Simple — it's just geometry, nothing to misinterpret
Fine for final parts — if the design is done and only needs printing

STL's limits:

Not editable — the provider can repair or scale it, but not change features
Resolution-dependent — export too coarse and curves look faceted
No units — occasionally causes scale confusion between tools

STEP: Precise, Editable CAD

A STEP file (.step / .stp) is a boundary-representation CAD format that stores exact geometry — true curves, precise dimensions, and units. It's the neutral format engineers exchange between different CAD systems, and it's the better file to send a service bureau whenever you have it.

STEP's strengths:

Dimensionally exact — no facets, no approximation
Editable — the provider can add draft, thicken walls, or adjust features
Accurate quoting — exact volume and geometry make quotes more reliable

STEP's only real downside is that some mesh-based and artistic workflows don't produce it — which is exactly where STL or OBJ fit.

Which Should You Send?

Situation	Send
You have a CAD source and want accuracy	STEP
You expect engineering adjustments	STEP
Mesh model, sculpt, or scan data	STL (or OBJ)
Final part, print-only	STL is fine
Not sure	Send both — STEP + STL

For most functional engineering parts, STEP is the source of truth and STL is a useful backup. Sending both removes ambiguity and speeds up quoting.

Common File-Prep Mistakes

Exporting STL too coarse. Faceted curves print faceted. Use a fine/high preset.
Wall thickness below printable minimums. Most processes need ~0.8–1.2 mm minimum walls; confirm with your provider and our guide to choosing a service.
Open or non-watertight meshes. Gaps in an STL cause slicing errors — run a mesh-repair check before sending.
Wrong units. Always confirm mm vs inches; STL doesn't carry units.
Sending only STL when edits are needed. If the provider must change geometry, they need STEP.

Match the File to the Process

The right format also depends on the technology. High-detail SLA resin parts benefit from a finely exported STL or a STEP source so fine features survive; functional FDM parts are forgiving. If you're still deciding between processes, our breakdown of SLA vs FDM printing explains how each handles detail and tolerance.

Get a Quote With Your File

Once your file is ready, browse the directory and submit it directly to a provider. Send STEP when you have it, STL as a backup, and describe the material, finish, and tolerance you need. No account required — submit your specs and the provider contacts you.