I'm familiar with a 421G. The 412G, I've not heard of. The 421G is similar to the 431G but it doesn't chainstitch. So, that makes it an open arm version of the 401G, or really not much different than a 401A except that it's an open arm machine. It has the same hook and bobbin case as the 401A or probably the 401G so it won't chain.