Our thread adapters are composed of alloy and iron-chromium-nickel steel. They are corrosion resistant and finished in black oxide. Inside thread of 5/8-11 for an M11 .380 to an outside thread of 3/4-10 to fit an M11 9mm suppressor or other component. * The tip of your .380 barrel must be cut back to fit this adapter. Call if any questions on your application.