The RM4 and VM4 one-piece upper receiver fits all KWA RM4, VM4, and Ronin Tactical Series rifles, including the original Magpul PTS ERGs. (Not compatible with the KeyMod Rail, which fits to the fluted version of the upper which is not available for individual sale). The upper receiver appears as part 363 on the RM4 and VM4 Series diagrams.
