Blog · STEP · 29 Sep 2026 · 2 min read

Can AI find identical and mirrored parts in a STEP assembly?

Yes, and it is where an AI agent saves the most time: hundreds of drawings become far fewer. It is also where it can get a plate cut backwards. How the agent tells identical, mirrored and similar parts apart, and where a person must decide.

A steel assembly often contains the same plate many times, and just as often a plate and its mirror image. An AI agent can compare hundreds of parts in minutes and group the identical ones, so one drawing with a quantity replaces many drawings. It is where most of the time savings come from. It is also where a wrong group means a plate cut the wrong way round, so the agent needs the right method, and the last word stays with an experienced designer.

Three kinds of "the same"

Why volume is not enough

The first idea is to compare volumes. It is a good filter: parts with different volumes are certainly different.

But a part and its mirror image have exactly the same volume, the same area and the same bounding box. Volume can tell you which parts might be the same. It cannot tell you which ones are mirrored.

A method that works

  1. Filter by volume and bounding box size. Only parts that match go further.
  2. Compare the flat outlines. Lay each part flat and compare the 2D profiles, holes included. Different profiles: different parts.
  3. Check the 3D for handedness. For parts that pass step 2, check what is on one face only: bevels, countersinks, marking lines. If it is on the opposite face, the part is the mirrored version.
  4. Show the groups on the 3D model and have an experienced designer approve them before anything is renumbered.

Why step 4 is not optional

Some differences are not in the geometry at all. A part may be identical in the model but made differently in the shop, or a bevel may be added by hand on the drawing. The person who knows the job decides. The automation proposes the groups; it does not merge anything on its own.

When a mirrored part does not need its own drawing

A plain plate with nothing on either face can simply be turned over. Its mirror is the same part, so quantity two on one drawing is correct. The left-hand version is needed only when something makes one face different from the other.

Do and don't

Do

Don't

Related: merging identical parts and renumbering drawings, when a mirrored plate needs its own drawing.

Grouping is one of the checks we run on every project. If you want it done on your model, send us a file.

Related guides

STEP 2 min read

Can AI get plate thickness from a STEP file? Only if it measures the right way

Ask an AI agent for the thickness of every plate in a STEP file and it will answer, confidently. Whether the answer is right depends on the method it uses. Four methods compared, and the one we let it trust.

STEP 3 min read

When does a mirrored plate need its own drawing? Left-hand parts explained

In a mirrored assembly, some plates can just be turned over and some must be cut as a separate left-hand part. A bevel or countersink on one face decides it, and the flat outline cannot see it. The five verdicts our check gives, the 1 mm tolerance, and the copied part that passed four checks and would have been cut backwards.

STEP 3 min read

How to split a STEP multi-body into separate Inventor part files with the API

The STEP arrives as one part with hundreds of solid bodies. To draw each one you need one part file per body. The iLogic code that does it, why you never convert the client's file, and the traps: bodies looked up by index, gaps in the numbering, bodies that will not delete.