WeldEdges Op Property Editor

Merges or bridges pairs of boundary edges on a polygon mesh object.

To redisplay: Select the polygon mesh object, click the Selection button on the Select panel, then click the WeldEdges Op icon.

Distance	The tolerance for welding edges. As you increase this value, more pairs of edges get welded.
Target	Specifies which edges to weld, when an appropriate pair of candidates is found: Input Edges welds pairs of selected edges with each other. Other Edges welds each selected edge with an unselected edge. All Edges welds each selected edge with any other selected or unselected edge.
Angle > 90	Welds two boundaries only if the difference between their orientations is greater than 90 degrees. This prevents the zipping effect from welding pairs of edges that are not facing each other.
Grow Selection (from two edges)	Allows boundaries adjacent to the ones you picked to be welded as well. This option is only available when exactly two boundaries were picked. Turn this option off to weld only the two boundaries you picked.
Bridge	Controls the behavior for connecting edges. When this option is off, pairs of facing edges are merged. When on, pairs of edges get connected by polygons.