I have brought this up before. Today I was cutting some sheet metal and I thought I would bring it up again. I do so because I am still amazed at how I can cut a straight line in sheet metal as long as I want with this little pair of offset tin snips. I am not kidding, you could cut an eight foot by four foot sheet of metal in half with this little $25 tool. When I think of how long it took me to figure this out! I bought all the tin snips and shears that I could get my hands on that said it was for a straight line. These "Offset" snips are made in both "left" and "right" versions. I think this is where I got confused, "left and right" doesn't sound like "straight" line to me!
Well the thing is they will cut around a corner just fine and you need the left and right cut so you can go in that direction too. A quality pair of these offset snips will shave off a mm wide piece of metal without distorting the metal!
They handles are color coded with the yellow being straight, the red being left hand cut and the green being right hand cut. I VERY rarely use the straight ones, the offset seam to do everything I need.
The long cut I did was kinda crude so it may not look perfectly straight to you. But if you have a straight edge drawn line you can cut RIGHT ON IT making a cut darn near like a shear. The photo with the long cut is the one that has the pair of offset snips on it. The other snips are for example of other types.
Here is a pair of Offset snips.
They are the cats meow for working with tin.