Flat sheet-metal part for forming a cylindrically shaped contact cage having a receiving space for insertion of a contact in the plugging-in direction, wherein the sheet-metal part comprises the following: a. a basic shape having four edges (1a, 1b, 1c, 1d) and four corner portions (2a, 2b, 2c, 2d), of which two of the edges (1a, 1b) extend parallel to one another and each form a collar web (10, 20) extending in each case between two corner portions (2a, 2b and 2c, 2d, respectively); b. a plurality of contact lamellae, which connect one collar web to the other collar web, c. wherein each collar web has in the region of the respective one corner portion (2a, 2c) a projection extending the length of the collar web and d. wherein each collar web has in the region of the respective other corner portion (2b, 2d) a recess, e. wherein the path followed by the edge in the region of the projection of the respective collar web (10, 20) respectively extending the length of the collar web runs as follows: linearly along the edge (1a, 1c) of the respective collar web (10, 20), then arcuately in the manner of a curve around the respective projection in an arc of approximately 180° and then around an approximately 90° arc, f. wherein the path followed by the edge in the region of the recess of the respective collar web (10, 20) in which the recess is provided runs as follows: linearly along the edge (1a, 1c) of the respective collar web, then arcuately in the manner of a curve around an approximately 90° arc along the recess, characterized in that further around in an arc of approximately 180° while forming a projection and g. alongside the recess, the projection lies with its side edge that is oriented in the direction of the edge (1a, 1c) against the opposite side edge of the projection in the region of the 90° arc. a. a basic shape having four edges (1a, 1b, 1c, 1d) and four corner portions (2a, 2b, 2c, 2d), of which two of the edges (1a, 1b) extend parallel to one another and each form a collar web (10, 20) extending in each case between two corner portions (2a, 2b and 2c, 2d, respectively); b. a plurality of contact lamellae, which connect one collar web to the other collar web, c. wherein each collar web has in the region of the respective one corner portion (2a, 2c) a projection extending the length of the collar web and d. wherein each collar web has in the region of the respective other corner portion (2b, 2d) a recess, e. wherein the path followed by the edge in the region of the projection of the respective collar web (10, 20) respectively extending the length of the collar web runs as follows: linearly along the edge (1a, 1c) of the respective collar web (10, 20), then arcuately in the manner of a curve around the respective projection in an arc of approximately 180° and then around an approximately 90° arc, f. wherein the path followed by the edge in the region of the recess of the respective collar web (10, 20) in which the recess is provided runs as follows: linearly along the edge (1a, 1c) of the respective collar web, then arcuately in the manner of a curve around an approximately 90° arc along the recess, characterized in that further around in an arc of approximately 180° while forming a projection and g. alongside the recess, the projection lies with its side edge that is oriented in the direction of the edge (1a, 1c) against the opposite side edge of the projection in the region of the 90° arc.