Tonytrout on the Eovia forum for Hexagon just gave me an excellent way to make sure the points I want to weld are on top of each other. "You get the head nice and square facing you in orthographic view, select all the points on the join, and then in the object properties window set the SIZE to 0 (zero) on the axis perpendicular to the plane,(Hint: you have three (XY orZ) axis to choose from, the right axis to adjust to 0 is usually the one that has the smallest number in ) This lines up all the points, when you duplicate and weld the points are identical and weld. The beauty of this method is that you can accurately join the two halfs even after the centre line ponts have been messed around with. No matter how careful you are especially if you are using soft selections ,the centre line points always seem to get off centre."