Aims: The purpose of this study was to improve the properties of bone screws by using high quality amorphous diamond (AD) coatings. Especially, in the case of long and thin screws, high torques leading to screw failures might be avoided by hard, smooth AD coatings. Methods: First, we constructed an affordable bone screw torque test equipment corresponding to ASTM standard F543–00. In the preliminary testing, a dozen of cortical bone screws with a diameter of 2,7 and 3,5 mm and a length of 50 mm were used. A half of the set was coated with an amorphous diamond coating of 1 μm thickness using pulsed arc discharge technique. The insertion and removal torques of the screws in animal bone were measured. Furthermore, failure torques were recorded. Results: The insertion and removal torques for the coated screws were on the average 10–15% lower than for uncoated screws. In addition, this improvement increased further as the screws were installed deeper. In all the cases, the failure torques were 30–50% higher than the minimum values required by the standard. Especially, in the case of thin screws, the coating seemed to increase the strength of the screws as well. Conclusions: Based on the present results, AD coatings are very durable on bone screws and improve the insertion and removal properties. Since AD is very biocompatible and gives excellent corrosion resistance, the improvements are assumed to last even in the long term clinical use.