Spyder Shim Kit, perhaps a better way than changing springs to increase or lower your Spyder or Piranha's velocity is to simply swap the shim. The Shim Kit will allow Spyder and Piranha owners to adjust their velocity in approx. 10 fps intervals just by adding a different colored shim. The shim kit provides 6 color coded shims, or spring guides. Each colored shim can be matched with the provided chart to see roughly how your guns velocity will be affected. An inexpensive way to drop or raise your guns velocity instantly.