An I-Frame. It is a frame from wicked sporz or something, i dont reember the company name exactly. It has a .3 mm trigger pull That is ridiculously small, it is close to an angel, which is like the size of a human hair, or so I heard. It moves your grip frame forward 1 inch, to center the weight of your gun more, and provides a better feel. If you have money to spend, get an I frame and a vision eye. You will definatley need the vision eye to keep up with the trigger. The frame is around 160, and I think vision is pretty close to that. I garuntee you will be happy with both of these mods if you spring for them