We present detailed properties of fast magnetosonic shocklets (1000 km in size and amplitude of 10 times the background B-field values) observed in natural unbounded collisionless plasma by a fleet of four Cluster spacecraft at the quasi-parallel bow shock. We provide for the first time details of the internal structure of shocklets which have magnetic pulses shifted in time from the plasma density pulses, have localized regions with ion acoustic turbulence, and are shown to slow down and thermalize the solar wind ions. The shocklets emit weak electron plasma waves which are used to verify the plasma density profiles within the structure. They move with supersonic speeds (~250 km/s) and appear in the region with mixing of cold solar wind ion beams and thermalized heated plasma. We provide a qualitative explanation for the observed relationship between the magnetic field and plasma density profiles within the structure based on a nonlinear momentum conservation equation of plasma fluid dynamics.