direction defined by a longitudinal axis of symmetry a the tubular member 15 also comprises a through hole 17 crosswise to the axis a as seen in fig2 and 3 a second end 15 b of tubular member 15 rests against the wall 12 and the transverse through hole 17 is aligned with a through hole 18 fig2 in the outer body 11 so that the pin 19 need simply be inserted inside the coaxial holes 18 and 17 to connect the tubular member 15 integrally to the outer body 11 the pin 19 is advantageously provided with a substantially u shaped spring member 20 for preventing in known manner accidental withdrawal of the pin 19 from the holes 17 18 as stated when not inserted inside the holes 17 and 18 the pin 19 may be housed inside the opening 12 a a threaded shank 21 a of a rod 21 is screwed inside the threaded seat 16 the rod 21 further comprises a head 21 b having a seat 21 c for housing a spherical joint 22 into which the pin p 2 best seen in fig1 is inserted as stated to connect one end of the strut 10 integrally to the support s at the end near the spherical joint 22 therefore by lifting the spring member 20 and removing the pin 19 from the through holes 17 18 the tubular member 15 is allowed to float freely inside the cavity 13 this capability is advantageously employed in certain operating modes of the tractor as when working on a field in a similar manner the cavity 14 in the sleeve 11 b houses a tubular member 24.