How to MIG weld? What size welding wire should I use? Is MIG or TIG better? What is the best gas for MIG welding? How much gas?... are just some of the questions I regularly get asked about welding; so, as a great way to put off welding up John's rusty Range Rover chassis I thought it might be good to do a bit of a MIG welding refresher. Here's everything you wanted to know about welding but are too cool to ask.