An annular packer (10) for use with an annular blow out preventer (20) formed of a plurality of blades or elements (21,30,72) where each of the blades (21,30,72) is curved and arranged in the annular bore such that the curve of the blade is not parallel with the longitudinal axis of the assembly. This creates an “iris” type of geometry which, as the iris closes, the annular bore (24) transforms from a parallel cylindrical shape to a smaller bore with a shape having at least one waist or pinch point (32,34,73,75) of smaller cross-section.