Merco M77 Threadmaster Full Density Threadseal Tape, made in the USA! Meets the new and current Mil Spec A-A-58092. No, really, the REAL mil spec, A-A-58092! This one is our pride and joy. Our M77 Threadmaster is flying around in Boeing airplanes, tested in NASA Research facilities, swimming on and under the oceans in ships and submarines from various ship-yards and places where you simply can't tolerate any discrepancies in specs and quality. M77 is 3.5 mils thick and offers a specific gravity 1.2-1.55 g/cc (the spec calls for 3.5 mil and 1.2 g/cc). We label both two sides with specs, relevant installation instructions, our eye-catching brand name graphics and of course an American flag. By the way, the spec T-27730A has been outdated since 9 Feb 1998. Don't fall for that T spec as an indication of any quality. There are a lot of products that only meet T-27730A, like our M66 for instance but having the spec does not guarantee quality. The spec was put into place in 1964, well before imports and low density products came to market. In fact that spec basically said if the tape is made of PTFE, and is white, it meets the spec. No indication of purity, of thickness or specific gravity.