AEROSHELL 33MS Lithium Moly Synthetic MIL-SPEC Barrel Nut Thread Grease, 1 oz Jar Improved anti-wear and corrosion resistance over AeroShell Grease 17. Fully approved to MIL-G-21164D. Prevents thread galling. Prevents the aluminum upper from welding itself to the steel barrel nut under the extreme heat and pressure of use. Approved for AR 15 rifle builds.