Sleeve for increasing retention value of a screw

Sleeve for increasing the retention value of a screw (7) in a structural component, said sleeve being axially elongated and having a leading end to be inserted first into a bore and a trailing end, said sleeve having an exterior surface and an interior surface, said exterior surface having a radially outwardly extending external thread (4, 24) terminating in a radially outer tip of constant external diameter with a thread pitch (H), said interior surface forming an axially extending internal bore (3, 23) including an internal thread (5, 25) at least in an axially extending section adjacent the trailing end of the sleeve, said internal thread having a thread pitch (H) the same as the thread pitch (H) of the external thread, wherein the improvement comprises that said internal bore (3, 23) tapers inwardly from the trailing end toward the leading end and in the trailing end-leading end direction said external thread (4, 24) follows said internal thread (5, 25) and said external thread (4, 24) and internal thread (5, 25) are offset in the trailing end-leading end direction by half (h) the thread pitch (H).