Simply put, this will replace the somewhat lanky looking stock pusher on the sledgefire, and can take much heavier springloads that quite literally launch shells out when opened. For this you need a fairly standard sized Nerf screw, and if you're using this file you probably already have a couple lying around. A wide, flat head is better, as the screw is used to hold onto the spring.
I did this solely because I was afraid of the plastic hook snapping, and the pusher used to bend. This new one is also much thicker for strength, with a flared base designed to grasp and hook out any shell type. The extra width helps to ensure that it does not get stuck in the grooves between stock shell dart chambers, and depending on your printed shells you may wish to sand this lower, say if it grazes your MEGA or RIVAL ammo too hard on firing.