can be used provided they be heat petroleum and chemical resistant and provide an adequate seal the plug is constructed of a cylindrical body member 13 which has a concentrically positioned male cylindrical plug 11 extending away from the body member 13 the smaller diameter of the plug defines a shoulder 12 at the intersection of the body 10 and the plug 11 which shoulder will abut the endmost edge of the line or tube when inserted the cap 20 is preferably constructed of a resilient plastic compound other materials can be used provided they be heat petroleum and chemical resistant and provide an adequate seal the cap 20 is constructed of a cylindrical body member 23 which has a concentrically located longitudinal bore 21 the back plate 22 is circularly shaped and is situated to have the same centerline axis of the cylinder 23 and the bore 21 the concave end of the bore 21 forms a tapered stop to about the endmost edge of the fitting or tube when installed plugs 10 and caps 20 both male and female have colors diameters and lengths defined within specified ranges and tolerances thus the colors and dimensions of the invention may be varied from those given below without departing from the scope or application of the invention these plugs 10 and caps 20 can be injection molded as a single piece of plastic compound the cylindrical body member 13 of the male plug has an outside diameter of 0 500 inches and a length of 0 500 inches the cylindrical plug portion 11 of the.