we make them out of stainless and they run the length of the bag and wrap from under the bottom and a tiny bit up the face of the bag .We glew them on and havent lost one yet and they get some serious damage .
I have two pairs of sinister skids if you're interested but they are just for the corners. I made mine out of a $5 piece of 1/4" x 1/2" x 18" steel from Home Depot. The spark is probably pretty boring but they've saved my 6" bags on several occasions already.
I figured my pipes would hit first. When we got to our first stop I was laughing at my buddy because i watched him drag his pipes around a few corners and he's pretty anal about his stuff, that's when he told me I was leaving white lines around the corners. I figured I was aired up and wouldn't even come close.