Polyaxial bone screws include a receiver and a shank, the receiver having in inner concave surface defining a spherical void and the shank having an upper spherical portion, the shank upper portion and receiver concave surface being in moveable friction fit engagement prior to locking of the shank with respect to the receiver. The receiver includes a circular edge formed by a spheric section, the edge capturing the shank upper portion within the receiver. Bone screws may include pressure inserts, shank upper portions having separate retainer rings, receiver arms having break-off extensions, and one or two-piece closures.
