Hi IStonia,
I think Nvil weld tool can have this option, just like the "Select Similar Facing" tool. So the threshold value can be adjusted while we press the hotkey and the welding will happen in real time.
This will be useful in the situation like shown in the picture below. Currently the best tool I find to perform this is Weld to Nearest, but it also welds some unwanted vertices if I don't do a more accurate selection.
(https://www.dropbox.com/s/c6katkhx327tvtm/nvil%20weld.jpg?raw=1)
Thanks kevjon for replying, I do aware of the those options. The autoweld you mentioned do gave me an idea to try out another way of merging the vertices, I was expecting to be able to merge the vertices by scaling them to the mid center but I found that autoweld doesn't work in this case.
(https://www.dropbox.com/s/brj4jp1ssyik9bi/scale%20vertices%20to%20middle.jpg?raw=1)
still.. even if it works, it's a bit slow, if I have first selected the vertices correctly just like the image above, Weld to Nearest would work nicely. My idea is if we can make a rough selection instead, and let the program weld the vertices based on threshold, and instead of typing the threshold manually (might need to try different values a few times), we can use mouse gesture to set the threshold and adjust it realtime, that would be more streamlined.