1. A MACHINE FOR FORMING PLASTIC JACKETS AROUND THE INTERSECTIONS BETWEEN LONGITUDINAL AND TRANSVERSE RODS OF STRUCTURAL STEEL MATS OR THE LIKE, COMPRISING MEANS FOR GUIDING AND SUPPORTING A SERIES OF LONGITUDINAL RODS IN A COMMON PLANE SO THAT AT LEAST ONE TRANSVERSE ROD MAY BE LOCATED IN A POSITION IN WHICH IT INTERSECTS SUCH LONGITUDINAL RODS AT POINTS WHICH ARE ARRANGED IN A ROW; MEANS FOR FEEDING TRANSVERSE RODS INTO POSITIONS FOR ATTACHMENT TO LONGITUDINAL RODS; A PLURALITY OF SEPARATE JACKET-FORMING UNITS EACH COMPRISING A PAIR OF NORMALLY SPACED MOLD SECTIONS LOCATED AT THE OPPOSITE SIDES OF SAID PLANE, AT LEAST ONE MOLD SECTION OF EACH PAIR BEING MOVABLE TOWARD THE OTHER MOLD SECTION TO DEFINE THEREWITH A MOLD CAVITY WHICH RECEIVES ONE OF SAID POINTS OF INTERSECTION; ACTUATING MEANS FOR RECIPROCATING SAID ONE MOLD SECTION OF EACH UNIT; AND MEANS FOR ADMITTING PLASTIC MATERIAL INTO SAID MOLD CAVITIES.