Features: Fits standard AEG hopups and barrels Best application: Working with a R-Hop, perfect fit, & No-Sanding, Available in our store. We have developed a full line of Custom-Cut R-Hops for various Tightbore Barrels, I.E., Prommy, PDI, EdGI, Madbull, ZCI. You can also use it for Flat-Hopping. It provides more consistent contact and backspin on BBs than normal bucking. Improve accuracy, range, grouping, and air seal. Suitable for .25g BBs and heavier Includes a Flat Nub Hardness: 55-60 degrees