Mirror a part

Give a rocket a matched pair of fins, boosters or wings on either side, linked so that moving, resizing or deleting one carries the other with it.

Use this whenever a ship needs the same part twice, evenly either side of its centre: a pair of fins, radial boosters, or landing legs.

Before you start

The part is already placed, hanging off the side of another part rather than sitting on the ship's own centreline.
It has no mirrored twin yet.

Tap the part to select it. Its properties sheet opens with three buttons: Rotate, Flip and Symmetry.
Tap Symmetry. A mirrored copy appears on the opposite side of whatever the part hangs from, facing the right way with no further adjustment.
Symmetry is greyed out here because this fin already has a linked twin. The starter rocket's two fins are joined exactly this way.

What you should see

Two copies of the part now sit either side of the ship. Move, rotate, resize or delete either one and the other follows, because a symmetry link ties them together for as long as both exist. Symmetry greys out on a part that already has a linked twin. That is what it looks like on the starter rocket's own two fins.

Note

Symmetry adds a full linked copy on the other side. Pressing M while dragging a part, or tapping Flip on its sheet once it is placed, does something different: it mirrors that one part where it already stands, with no copy and no link.