A tulip assembly configured to be coupled to a head of a bone fixation device includes at least one inner member configured to fix the tulip assembly to the head of a bone fixation device, and an outer member including at least one engagement surface configured to selectively fix a rod in the tulip assembly...http://www.google.com.au/patents/US8016866?utm_source=gb-gplus-sharePatent US8016866 - Pedicle screw system with provisional locking aspects
