Select an Edit Poly or editable poly object. > Modify panel > Vertex or Edge sub-object level > Edit Vertices/Edges rollout
> Weld Settings button
Select an Edit Poly or editable poly object. > Vertex or Edge sub-object level > Quad menu > tools 2 quadrant > Weld Settings
button
Use this dialog for setting the weld threshold for vertices and edges.

Weld Threshold—Specifies the maximum distance, in scene units, within which selected sub-objects will be welded.
Any vertex or edge that lies outside this threshold (that is, it's farther than this from the nearest vertex or edge) will not be welded.
Number of Vertices—Shows the number of vertices before and after the weld.
The After quantity updates dynamically as you change the setting with the spinner.