Fastening system for fastening a dental prosthesis to a dental implant having a ball shaped portion, wherein the fastening system comprises an external sleeve adapted to form part of or support a dental prosthesis, the external sleeve being provided with a bore extending along a bore axis through the external sleeve, a manoeuvring member being received in a first portion of the bore and being rotatable in the bore about the bore axis, a gripping member being received in a second portion of the bore, the gripping member being provided with a body portion and a seat portion, the seat portion having a seat adapted to grip around said ball shaped portion of said dental implant, wherein the bore is provided with a radially inwardly extending shoulder portion adapted to interact with a radially outwardly extending shoulder portion of the manoeuvring member thereby preventing the manoeuvring member from moving in the bore from the first portion to the second portion, wherein the manoeuvring member and the gripping member are provided with obliquely oriented mutually interacting surfaces (20e, 30a') such that rotation of the manoeuvring member causes the gripping member and the manoeuvring member to move relative to each other along the bore axis, characterised in that the seat portion of the gripping member is provided with a circumferentially extending wall extending around the seat, wherein the wall is provided with at least two slits (33a, 33b), each slit (33a, 33b) having a transverse extension through the wall from an inner surface of the seat to an outer surface of the seat portion and each slit (33a, 33b) having a longitudinal extension with a major extension along the bore axis from a mouth portion (m 31) of the seat towards the body portion, wherein the slits (33a, 33b) divide the wall, as seen along the circumference of the wall, in at least two wall portions (32a, 32b), which wall portions (32a, 32b) are interconnected via the body portion, thereby allowing the wall portions (32a, 32b) to resiliently flex towards each other when subjected to an inwardly directed force, wherein the wall portions have outwardly facing abutment surfaces (32a', 32b') tapering towards the first portion of the bore, wherein the second portion of the bore has an inwardly facing abutment surface being adapted to interact with the outwardly facing abutment surfaces (32a', 32b) of the wall portions (32a, 32b), whereby rotation of the manoeuvring member is adapted to pull the gripping member towards the first portion of the bore such that said abutment surfaces (32a', 32b') interacts and forces the wall portions (32a, 32b) resiliently towards each other, the fastening system thereby being adapted to clamp onto said ball of said dental implant. an external sleeve adapted to form part of or support a dental prosthesis, the external sleeve being provided with a bore extending along a bore axis through the external sleeve, a manoeuvring member being received in a first portion of the bore and being rotatable in the bore about the bore axis, a gripping member being received in a second portion of the bore, the gripping member being provided with a body portion and a seat portion, the seat portion having a seat adapted to grip around said ball shaped portion of said dental implant, wherein the bore is provided with a radially inwardly extending shoulder portion adapted to interact with a radially outwardly extending shoulder portion of the manoeuvring member thereby preventing the manoeuvring member from moving in the bore from the first portion to the second portion, wherein the manoeuvring member and the gripping member are provided with obliquely oriented mutually interacting surfaces (20e, 30a') such that rotation of the manoeuvring member causes the gripping member and the manoeuvring member to move relative to each other along the bore axis, characterised in that the seat portion of the gripping member is provided with a circumferentially extending wall extending around the seat, wherein the wall is provided with at least two slits (33a, 33b), each slit (33a, 33b) having a transverse extension through the wall from an inner surface of the seat to an outer surface of the seat portion and each slit (33a, 33b) having a longitudinal extension with a major extension along the bore axis from a mouth portion (m 31) of the seat towards the body portion, wherein the slits (33a, 33b) divide the wall, as seen along the circumference of the wall, in at least two wall portions (32a, 32b), which wall portions (32a, 32b) are interconnected via the body portion, thereby allowing the wall portions (32a, 32b) to resiliently flex towards each other when subjected to an inwardly directed force, wherein the wall portions have outwardly facing abutment surfaces (32a', 32b') tapering towards the first portion of the bore, wherein the second portion of the bore has an inwardly facing abutment surface being adapted to interact with the outwardly facing abutment surfaces (32a', 32b) of the wall portions (32a, 32b), whereby rotation of the manoeuvring member is adapted to pull the gripping member towards the first portion of the bore such that said abutment surfaces (32a', 32b') interacts and forces the wall portions (32a, 32b) resiliently towards each other, the fastening system thereby being adapted to clamp onto said ball of said dental implant.