AeroShell 64 (previously 33MS) aerospace grease that meets mil-spec MIL-G-21164D for barrel nut and receiver extension assembly on AR platform upper and lower receiver threads. As used on complete Umbrella gov/military sample builds, offered here in .5oz or 1oz for your own barreling and lower building projects. AeroShell 64 (Formerly 33MS) Military Specification While this grease is perhaps best known for meeting rifle build mil-spec, it's a superior grease for any of your lubrication needs, from home projects to industrial applications, you're covered.