A system for lockably engaging bone screws into a fixation plate may include a locking fixation plate including a threaded screw hole defined by an inner surface surrounding the threaded screw hole, the inner surface comprising an upper countersink and a threaded portion, the threaded portion comprising a pair of threads arranged in a double helix configuration, and a screw comprising a generally conical head tapering into a generally cylindrical shaft that ends at a tip and a single thread beginning near the tip and extending along the generally cylindrical shaft and onto the generally conical head, a thread height of the single thread being constant over a majority of the generally cylindrical shaft and tapering as the thread extends onto the head.