A
fastener (1) comprises at least two
fastener halves (3A, 3B) each of which comprises a main body (7A, 7B) and a finger (9A, 9B) depending therefrom, the finger (9A, 9B) being spaced apart from the main body (7A, 7B) so as to define a recess (13A, 13B) between the body (7A, 7B) and the finger (9A, 9B). The recess (13A, 13B) receives, in use, the finger (9B, 9A) of the other
fastener half (3A, 3B) to fasten the fastener halves (3A, 3B) together. At least one of the recess (13A, 13B) of one fastener half (3A, 3B) and the finger (9A, 9B) of the other fastener half (3A, 3B) comprises a concave
mating formation arranged to engage in use with a convex
mating formation (15A, 15B) provided on the finger (9A, 9B) of the other fastener half (3A, 3B) or on the recess (13A, 13B) of the one fastener half (3A, 3B) respectively. The formations are arranged to
resist, when so engaged and under tension in use, the fastener halves (3A, 3B) unfastening in a direction away from the longitudinal axes of the fastener halves (3A, 3B).