Stitch

When imported geometry (sheet parts) are unconnected or have small sections that overlap, use the stitch operation to ensure mesh connectivity.

Sheet parts that are within the specified tolerance are considered to be connected and meshed correctly.

The stitch tool can lead to strange geometry display in CADFEKO due to the tolerance of edges, faces and nodes being large and displayed anywhere within the tolerance area. The mesh does not suffer the same display issues since the mesh elements have a very small tolerance.
Note:

Use the stitch operation as a replacement for the union operation for sheet parts that have small misalignments or imperfections (usually introduced through CAD translation).

The stitch operation is generally faster and more efficient than the union operation, but is limited to sheet bodies and introduces a tolerance (small uncertainty in the exact geometrical location).