Today I noticed that games such as Defaultio's in progress game has a welding tool that can detect where two parts meet and you can apply a little weld at that point. I have done some research into how this was accomplished and could not understand exactly how he was able to figure out these points that could be welded. The game in it's current state is here if you need to see what I am trying to have someone explain to me.
http://www.roblox.com/games/171119765/epic-game
** Game may be closed as he is working on it currently **