By this amendment, Appendices A and B to Part 192 are modified tb incorporate by reference the 1970 and 1971 editions of the American Society for Testing  materials (ASTM) Specification D2513, "Standard Specification for Thermoplastic Gas Pressure Pipe; Tubing, and Fittings". Also, two changes to § 192.59 are made. First, the use of special sizes of plastic pipe is permitted where pipe of a diameter included in a listed specification is impractical to use. Secondly, plastic pipe manufactured after Mlarch 21, 1975,is qualified for use only if it is manufactured in accordance with the latest listed edition of a listed specification. Listed specifications are those in Section I of Appendix B. This amendment is based on a notice of proposed rule making (Notice 74-2) issued by the Director, Office of Pipeline Safety (OPS), on April 16, 1974, and published at 39 FR 14218. Interested persons were given an opportunity to comment on the proposed rule changes by submitting written information-views, or arguments by June 3, 1974. The comments received have been fully considered in developing the final rules.