Symmetry in SOLIDWORKS doesn't mean just one thing. There are four levels, ranging from a sketch line to a complete part, and choosing the wrong one wastes time or breaks the model update. The trickiest case, the one that comes up time and time again, is the left/right part. We’ll get to that.
- There are 4 levels of symmetry In SOLIDWORKS: sketch, feature, body, part.
- A piece that is symmetrical by nature → sketch symmetry relationship (Only half is scored.).
- Repeated detail on opposite sides → functional symmetry (remains linked to the original).
- Solid, multi-body, or mold → body symmetry.
- Left/right part to be manufactured → Symmetry of a Part (Mirror Part), not a single copy has ever been returned.
Level 1: Symmetry in the Sketch
The simplest level. In a sketch, you draw half of it and mirror the rest. Symmetry relates two entities with respect to a construction line: they remain symmetrical no matter what. This is the appropriate method when the part is inherently symmetrical. You dimension only one side.
The Entity Symmetry feature mirrors geometry that has already been drawn, which can be useful in certain situations. Dynamic symmetry (Tools > Sketch Tools > Dynamic Symmetry) mirrors in real time as you draw: handy for highly symmetrical profiles, but otherwise confusing.
Simple rule: If the part is symmetrical, sketch half of it and define a symmetry relationship. You can then halve the dimensions, and the model will remain editable.
Level 2: Symmetry of Functions
You have created a hole, a boss, or a fillet on one side. The Symmetry feature (Insert > Repeat/Symmetry > Symmetry) copies it to the other side of a plane. The advantage over sketch symmetry is that the mirrored feature remains linked to the original. If you modify the source hole, the mirrored hole updates accordingly. This is ideal for repeated details that are mirrored across the same part.
Level 3: Body Symmetry
When you need to mirror an entire solid rather than a single feature, you mirror the solid. Use the same command by checking the "Mirror Solid" box. SOLIDWORKS creates a second mirrored body within the same part. This is useful for multi-body parts, molds, and geometries where one half is too complex to be re-defined function by function.
Level 4: The Left/Right Mirror Room and Its Trap
The classic scenario. You have a part, and you need its mirror image: a left bracket and a right bracket, two symmetrical housings. The natural instinct is to copy the part and flip it in the assembly. That’s a mistake.
A part that is flipped in the assembly remains the same part. Same part number, same file, same actual orientation. During manufacturing, you produce the same side twice; you never produce the opposite side. The assembly won’t fit.
The correct method: Insert > Mirror Part. You select a plane, and SOLIDWORKS generates a new, truly mirrored part file linked to the original via a reference. When you modify the parent part, the mirrored part updates accordingly. Two distinct parts, left and right, with two separate references for the bill of materials and the shop floor.
My position: Whenever a mirror-image part needs to be manufactured separately, it should be the symmetry of the original part, never a flipped copy. A flipped copy is only used for visualization, not for production.
The Right Level at the Right Time
Internal symmetry within a symmetrical part: sketch relationship. Repeated detail on opposite sides: function symmetry. Entire volume within a multi-body part: body symmetry. Opposite part to be manufactured: part symmetry. You won’t notice the wrong choice right away. You’ll realize it when the modification doesn’t propagate, or, worse, on the shop floor.
Do your teams want to improve their skills in these methods? Ohmycad is a SOLIDWORKS-certified training center.
In the same series: SOLIDWORKS Sheet Metal Tables and Master 3D Sketching.
Frequently asked Questions
How many types of symmetry are there in SOLIDWORKS?
Four: sketch symmetry, function symmetry, body symmetry, and symmetry of a complete part (Mirror Part). Each corresponds to a different level of the model.
How do you create a left part and a right part in SOLIDWORKS?
Via Insert > Symmetry of a Part. SOLIDWORKS generates a new, truly mirrored file that is linked to the original via a reference, with its own reference for the bill of materials.
Can we just flip the part over in the assembly?
No. A flipped part remains the same file, the same actual part: during manufacturing, the same part is produced twice, and the assembly doesn't fit. The flipping is only for visualization purposes.
What is the difference between function symmetry and body symmetry?
Functional symmetry mirrors a detail (hole, boss, fillet) to the other side of a plane; body symmetry mirrors an entire solid within the same part, which is useful in multi-body models or for a mold.
Does the mirror image update if I modify the original?
Yes: The mirror part remains linked by reference to the parent part and updates correctly.
