Each of the Merge tools adds a preprocessing step to the optimization process. These can help correct specific problems in a model.
When on, merges vertices before performing the optimization. Default=off.
ThresholdSets the distance within which vertices are merged. This distance is based on a percentage of the size of the object’s bounding box. At the Threshold value of 0.0, the distance is about 0.0001 percent of the bounding-box size. At the Threshold value of 100.0, the distance is about 5 percent of the bounding-box size. Range=0.0 to 100.0. Default=0.0.
When on, merges coplanar (or nearly coplanar) faces before performing the optimization. Default=off.
Threshold AngleSets the angle between face normals within which faces are merged. Range=0.0 to 10.0. Default=0.0.
Original model
Vertices: 557
Merge Faces turned off
Vertex % = 25.0
Vertices: 139
Faces: 214
Merge Faces turned on
Vertex % = 25.0
Vertices: 23
Faces: 21
When a model has coplanar faces, Merge Faces can greatly improve optimization.