Coincident vertices are merged and normals are averaged at the merged vertices.

This tool is only needed in rare cases. For example, a file imported from a different system, in a format other than STL, could have all its shared vertices stored twice. This could be detected within the Mesh Repair tool by the presence of a red boundary surrounding each triangle. In that case, the vertices must be merged with Mesh Weld Vertices before using any other Mesh tool.