The tip cap(1) comprises: a closed distal end portion (3)having a transverse proximal surface(5) a peripheral skirt (7) extending in the proximal direction from said proximal surface (5) and having an inner surface (10) designed to cooperate with the outer surface (31) of the injection device tip(27) a nipple (11)protruding from said proximal surface (5)and designed to engage the injection device tip(27). The inner cavity (14) of the tip cap is such that: the outer fillet (16) has a radius of curvature ranging from 0 4 to 0 6mm the inner fillet (17) has a radius of curvature ranging from 0 25 to 0 35mm the nipple base width ranges from 1 4 to 1 6 mm the dome shaped proximal portion (13) of the nipple (11) has a radius of curvature ranging from 0 55 to 0 70mm.
