sheet metal gauge help please?

sheet metal welding is motsly about prep. I found early on that its easy to blow holes if you don't have it set completely flat, or gapped just right or if the metal is thinner than you think it is. I discovered that when I ws grinding down the surface to clean metal before welding, I was actually removing too much metal. Patience and diligence is the key. don't get in a hurry. make sure its right before you start welding. Thats wha tkaes all the time, welding goes quick in comparison