Aim. Distal locking screw deformation is frequent in interlocking nailing of femur fractures. For today's clinical application applying two distal locking screws together is mostly used method. The aim of this study was to research whether second distal locking screw is necessary in interlocking nailing of femur fractures or not. Methods. A metal cylinder which has 37 mm internal diameter was prepared representing distal femur. A 3-point bending test was performed on 4 types of screws with 2 different dimensions (5 mm and 5.5 mm) and with 2 different screw geometries (threaded and unthreaded) in single for 10 pieces or double application for 20 pieces each. We determined the yield points of the screws applied single and the determined yield points of the screws applied double at 3 point bending tests. Results. We found that 5 mm diameter smooth screw applied single (1567±362 N, 1308-1826 N) (mean±SD, 95% CI), 5.5 mm diameter threaded screws applied single (1556±247 N 1379-1733 N) and 5.5 mm diameter smooth screws applied single (2060±417 N 1767-2359 N) showed two times more bending resistance than 5 mm diameter threaded screws applied double 713±310 N (573-863 N). Conclusion. Five mm diameter smooth distal locking screw applied single or 5.5 mm diameter threaded screw applied single or 5.5 mm smooth screw applied single must be preferred instead of 5 mm diameter threaded distal locking screw applied double. This prospective comparative study has an evidence grade level of II.