Intrnal threads one end: 3.250-6un-2b x 1.250 in; external threads other end: 3.250-6unr-2a x 2.580 in; entire surface is coated with thin layer of corrosion preventive compound conforming to mil-prf-16173, class ii, grade 2, then wrapped securely with greaseproof barrier material conforming to mil-prf-121, type ii