Abstract: A spring loaded, tamperproof plug valve such as a pressure gas stop has the rotatable valve plug resiliently retained against removal from the valve body by two stacked, slit, frustoconical, transversely arched spring washers that have teeth which make a one-way tight friction fit on a projecting end portion of the valve plug, and the outer peripheral portion of the forward of the two washers bears on a recessed planar area of the valve body which is surrounded by a continuous boss so a prying tool cannot be inserted beneath either washer. A self-threading sheet metal nut forms a thread in a reduced extremity of the valve plug and has a concentric integral skirt which bears on the teeth and also on the crown of the arched slit washer. The plug can be removed only by destroying the washer or the valve, either of which renders it inoperative. The nut will strip before the spring washers can be compressed enough to "lock" the plug in the valve body.