arc of 180 u00b0 or less but in any event will be sufficiently large to support the projecting elements also shown in fig2 is a mandrel 24 which is comprised of a transversely cut mating cylindrical section preferably mold piece 16 is constructed of copper the mandrel may be constructed of steel or any other material which is suitably treated to resist adhesion to the injected molding compound in accordance with the present invention the projecting elements 20 are first inserted into the ends of tubing 12 clamps or jigs may be used to advantage for aligning and holding the end of the collector tubing stationary while elements 20 are inserted in the tubing mold piece 16 and mandrel 24 are then placed in abuttment in an injection or compression mold as shown in fig3 a and 3b identical reference numbers are used in all figures for corresponding elements to ease in understanding the invention a lower mold housing 30 only is shown in fig3 a whereas an upper mold housing 32 and lower mold housing 30 are shown in fig3 b as shown in fig3 a the ends of the mold piece 16 and mandrel 24 sealingly abut the innerfaces 34 and 36 of the mold housing such an arrangement will necessarily result in a molded header having two open ends in a preferred embodiment of this invention one end of the male plug is offset from the inner mold wall face such an arrangement will result in a header having a single open end sidewall 38 of the mold has a plurality.