1. A tool insert for insertion into a body of a patient through an operating channel of an endoscopic instrument , 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 of the instrument , 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 of the instrument , 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. <EOS>