Applies to neck threads of gas culinders and to the material, outlet threads and dimensions of valve fittings for compressed gas cylinders in general use and for portable cylinders under 25 lb water capacity. It also applies to the cylinder neck thread and the outlet thread of cylinders employing screwed outlet connections and used for medical purposes, but it does not apply to yoke outlets for medical gas cylinders which are covered in AS CB4, Supplement No. 1. Recommendations for inspection gauges are included in Appendix A.