Plug-in insert designed for insertion into a main body, wherein the plug-in insert is designed for the releasable coupling of a tubular element in the main body, wherein the plug-in insert has a plug-in sleeve, a fixing element and a release member, wherein the fixing element is designed for the releasable fixing of a tubular element, inserted via an insertion opening, in the plug-in sleeve and the release member cooperates with the fixing element in such a way that the fixing of the tubular element is released by an axial movement of the release member relative to the plug-in sleeve, wherein the plug-in sleeve comprises a sleeve portion (5.1) formed of at least one wall element (5A, 5B), wherein the wall element (5A, 5B) is formed by stamping and bending a metallic flat material portion into a shell-shaped or circumferentially closed member, wherein the plug-in sleeve has, at a second free end, opposite to the insertion opening, a flange (5.1.2) for forming a contact surface for a sealing element, by means of which the transition between the tubular element and the main body is sealed, wherein: - fixing members formed integrally with the plug-in sleeve are provided for fixing the plug-in sleeve in the main body, wherein the fixing members are provided for fixing the plug-in insert in the main body, and wherein the fixing members ∘ are formed by a plurality of claws (5.1.3) arranged so as to be distributed circumferentially over the plug-in sleeve and the claws (5.1.3) are provided in the region of the flange (5.1.2) ∘ or by at least one rib (5.1.7), wherein the plug-in sleeve has a bead (5.1.1) in which the fixing element is held at the edge and wherein the outer wall portion of the plug-in sleeve forms, in the region of the bead (5.1.1), the at least one rib (5.1.7) or includes the rib (5.1.7); or - wherein the plug-in sleeve is designed to be fixed in the main body by forming an edge region (3.1) of the main body, wherein the plug-in sleeve has, at a first free end at which the insertion opening for the tubular element is provided, a collar portion (5.2.) which is formed by a separate collar element, wherein the collar element has, on the outer circumferential side, an inclined surface (8.5) or a shoulder (8.6) which is designed to be embraced by a formed edge region (3.1) of the main body in order to fix the plug-in insert in the main body. - fixing members formed integrally with the plug-in sleeve are provided for fixing the plug-in sleeve in the main body, wherein the fixing members are provided for fixing the plug-in insert in the main body, and wherein the fixing members ∘ are formed by a plurality of claws (5.1.3) arranged so as to be distributed circumferentially over the plug-in sleeve and the claws (5.1.3) are provided in the region of the flange (5.1.2) ∘ or by at least one rib (5.1.7), wherein the plug-in sleeve has a bead (5.1.1) in which the fixing element is held at the edge and wherein the outer wall portion of the plug-in sleeve forms, in the region of the bead (5.1.1), the at least one rib (5.1.7) or includes the rib (5.1.7); or ∘ are formed by a plurality of claws (5.1.3) arranged so as to be distributed circumferentially over the plug-in sleeve and the claws (5.1.3) are provided in the region of the flange (5.1.2) ∘ or by at least one rib (5.1.7), wherein the plug-in sleeve has a bead (5.1.1) in which the fixing element is held at the edge and wherein the outer wall portion of the plug-in sleeve forms, in the region of the bead (5.1.1), the at least one rib (5.1.7) or includes the rib (5.1.7); or - wherein the plug-in sleeve is designed to be fixed in the main body by forming an edge region (3.1) of the main body, wherein the plug-in sleeve has, at a first free end at which the insertion opening for the tubular element is provided, a collar portion (5.2.) which is formed by a separate collar element, wherein the collar element has, on the outer circumferential side, an inclined surface (8.5) or a shoulder (8.6) which is designed to be embraced by a formed edge region (3.1) of the main body in order to fix the plug-in insert in the main body.