Bought couple of these to increase the volume of my co2 mags for DH mod. Work well, and despite being "GMAG" gas magazine tanks, they do fit basic 7.62x39 style magazines lengthwise as well. What they do not fit into however, is the GHK ak GEN 1 co2 mags. The diameter of the threading is smaller on gen 2 mags even though the threads are the same. Heavy re-threading is required for the tubes if you want to fit them into gen 1 mags.