Thumb support or pinch grip are ways of holding the fork and ott means the elastic goes,,, over the top ,,,, as opposed to going ,,,,,,through the forks,,,,,, the one on the left is ttf ,,middle is looped tube,, and right is ott, it's simply how you prefer to attach your elastics, regarding ammo anything from 9mm steel through pebbles,[BANNED TEXT] nuts and 12mm lead try a few til you find one that suits you and your set up