This paper presents the experimental results of mechanical tests conducted on different types of fully threaded screws used in combination with various hardwood species. Screws were put on stage with a 45-degree-inclination and parallel arrangement. Push-out specimens with symmetrical configurations were fabricated using glulam beams and boards composed of three Italian hardwood types: beech, chestnut, and hybrid beech–silver fir. These species were used respectively as the central and side members of the specimens. Short-term tests under quasi-static monotonic loading were performed in accordance with EN 26891.

The primary objective was to evaluate the fasteners' stiffness, strength, ductility, and failure modes, in order to assess their suitability for application in hardwood timber-to-timber composite (TTC) floor systems. Experimental outcomes are presented and critically discussed. Additionally, theoretical models from the literature were applied to predict the ultimate load and slip modulus, allowing for a comparison with the experimental findings.

Among the configurations tested, screws in the hybrid beech–silver fir combination exhibited significantly higher ultimate load, stiffness, and yield strength compared to those in homogeneous beech or chestnut. The comparison with theoretical predictions revealed a general underestimation of load-bearing capacity and an overestimation of slip modulus, particularly in fully hardwood assemblies. The role of the head was significant for slidings greater than 12mm.