1. A tool insert for insertion into a body of a patient through an operating channel (15, 131) of an endoscopic instrument (1, 134), wherein the tool insert has: - a distal-side tool, - a proximal-side manipulation element, and - a control means, which is guided in a sheath, and by way of which the tool can be controlled by means of the manipulation element, wherein the control means extends between the manipulation element and the tool, wherein the manipulation element has an attachment element, a sheath control element, a spring element and a tool control element, wherein the attachment element has a connector for connection to an operating channel opening (39, 153) of the instrument (1, 134), wherein the sheath control element is coupled to the sheath, and an axial position of the sheath relative to the attachment element can be adjusted by actuation of the sheath control element, wherein the tool control element is coupled to the control means, and an axial position of the control means relative to the sheath can be adjusted by an actuation of the tool control element, wherein the spring element is arranged so as to exert a proximally-directed spring force on the tool control element, wherein the sheath control element has a larger outer diameter than the tool control element, and characterised in that, the sheath control element is screwed in the distal direction onto the attachment element, wherein the attachment element for the screwing-on of the connector has a first outer knurling, and the sheath control element has a second outer knurling for the adjustment of the rotational position of the sheath control element, wherein the sheath control element has a collar with a circumferential finger-traction surface, facing essentially in the distal direction, and the tool control element has a thumb-pressure surface, facing essentially in the proximal direction. - a distal-side tool, - a proximal-side manipulation element, and - a control means, which is guided in a sheath, and by way of which the tool can be controlled by means of the manipulation element, the control means extends between the manipulation element and the tool, wherein the manipulation element has an attachment element, a sheath control element, a spring element and a tool control element, wherein the attachment element has a connector for connection to an operating channel opening (39, 153) of the instrument (1, 134), wherein the sheath control element is coupled to the sheath, and an axial position of the sheath relative to the attachment element can be adjusted by actuation of the sheath control element, wherein the tool control element is coupled to the control means, and an axial position of the control means relative to the sheath can be adjusted by an actuation of the tool control element, wherein the spring element is arranged so as to exert a proximally-directed spring force on the tool control element, wherein the sheath control element has a larger outer diameter than the tool control element, and characterised in that, the sheath control element is screwed in the distal direction onto the attachment element, wherein the attachment element for the screwing-on of the connector has a first outer knurling, and the sheath control element has a second outer knurling for the adjustment of the rotational position of the sheath control element, wherein the sheath control element has a collar with a circumferential finger-traction surface, facing essentially in the distal direction, and the tool control element has a thumb-pressure surface, facing essentially in the proximal direction.