Merges selected edges and vertices that are within a specified threshold distance of each other. For example, two selected edges will be merged into one shared edge.
Edit Mesh > Merge Components > 
Merge Edges Options
The following options are available when edges are selected.
- Merge UVs
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Merges the UVs shared by the edges. If turned off, the UVs are not merged and can be manipulated and edited independently. The default setting is on.
Tip: Turn this option off if you have a model that is mapped with different textures on either side of where the edges merge. - Threshold
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Any selected edges further apart than this distance will not be merged. Set this value carefully. If it’s too small, no edges will merge. If it’s too large, the operation may merge unwanted selected edges. The default is 0.01.
Threshold distance
Determines the threshold distance between edges in different coordinate systems.
- World space
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(Default) Specifies that the Threshold value is the distance between edges in world space.
- Local space
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Specifies that the Threshold value is the distance between edges in local space.
Merge Vertices Options
The following options are available when vertices are selected.
- Threshold
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Any selected vertices further apart than this distance will not be merged. Set this value carefully. If it’s too small, no vertices will merge. If it’s too large, the operation may merge unwanted selected vertices. The default is 0.01.
- Always merge for two vertices
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When two vertices are selected, they are merged regardless of the Threshold value.