Interstage Couplers are used to house staging timers and to connect the upper and lower stages together. The Interstage 3000, the latest version from PML, is used in our two-stage rocket kits, but is now available for scratchbuilders designing their own staged rockets. Using an IS3000 system from PML is a quick, simple solution to an often-difficult design problem. Interstage 3000 kits are ready to ship in 2.2, 2.6, 3.0 and 4" diameters.