The compression strength of the differential screw is generated along the fracture line or nonunion due to the spacing adjustments between two bone fragments which occurs while turning the screw.
With each turn of a screwdriver the BSS screw advances 0.15 mm. The complete compression of the thread head requires advancing 0.6 mm over the fracture line or nonunion which ensures an excellent primary stability. At the discretion of the surgeon, the screw can be sunken further resulting in a greater compression. Warning: a greater compression causes an increased risk of an angular deformity in the case of an off-centered screw position or could lead to a shortening of the scaphoid in the case of nonunion.