The invention relates to a method for producing plastics containers (15) from thermoplastics with inserts (13) which, by exploiting the heat of plasticization, are connected during shaping of the plastics container (15) by a material bond and/or interlocking connection to the container wall (140), wherein the method provides the use of at least one opening (26) on the insert (13), which opening forms a melt duct or melt inlet and/or melt passage for plasticized or plastic material of the container wall (140), wherein the method is distinguished in that the opening (26) is monitored as a reference opening (26) by optical and/or sensory means during the production of the connection, wherein the degree of penetration of the opening (26) with thermoplastic from the container wall (140) is used as a measure of the quality of the connection.