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 (Z), wherein the sheet-metal part comprises the following: a. a basic shape having four edges and four corner portions , of which two of the edges extend parallel to one another and each form a collar web 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 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 a recess , e. wherein the path followed by the edge (K) in the region of the projection of the respective collar web respectively extending the length of the collar web runs as follows: linearly along the edge of the respective collar web , 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 in which the recess is provided runs as follows: linearly along the edge 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 against the opposite side edge of the projection in the region of the 90° arc . a. a basic shape having four edges and four corner portions , of which two of the edges extend parallel to one another and each form a collar web 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 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 a recess , e. wherein the path followed by the edge (K) in the region of the projection of the respective collar web respectively extending the length of the collar web runs as follows: linearly along the edge of the respective collar web , 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 in which the recess is provided runs as follows: linearly along the edge 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 against the opposite side edge of the projection in the region of the 90° arc . <EOS>