BT 4 (Combat, Erc, Delta, Elite) - Color Coded 3x Oring Rebuild Kit O-rings are color coded by size, eliminating the headache of matching up sizes. Included color/size chart helps with your first time rebuilding your marker. After that, just replace orings by color when it comes time to rebuild again. All of the o-rings you need to perform a standard rebuild of your marker three times (other quantities available).