Heavy recoil JP silent capture buffer spring. This is an H2 weight. Purchased for $210 and is able to fit any milspec AR15 tube. You will need the extra white filler piece if using for an AR10 sold on their website. I do have the thin aluminum piece they include for the milspec AR15 as pictured. I am firm on price, reason for selling is it did not work with my build and was used for less than 5 rounds due to being under gassed.