It is difficult to determine and control the tension level in a bolt; however, there is a great need for that to ensure safe operation of large structures. Bolts come in all sizes, but when properly tightened a bolt can roughly be considered an axially stressed clamped-clamped beam. A novel technique is proposed to quantify the level of bolt tightness by analysing natural frequencies and damping ratios of the bolt, based on simple hammer impacts. To study the application potential of the technique a set of real bolted joints, holding together machinery parts for a fluid mechanic setup, are impulse hammer impacted and the vibration response analysed. The tests aim to capture obstacles induced by working with bolts outside a controlled laboratory.