Collar for telescopic cylinder for tipper vehicles and telescopic cylinder with such a collar

A collar for a telescopic cylinder with a cap, said cap comprising a terminal portion that presents an opening of said cap, said collar comprising, in the following order:

• a first annular element with a contoured profile, which surrounds said terminal portion and is welded thereto,
• a second annular element, which can move with respect to said terminal portion and to said first annular element, said second annular element having at least two pins which extend at right angles to an external surface thereof, said second annular element surrounding at least partially said first annular element and said terminal portion, said second annular element being in contact with said first annular element, and
• an O-ring, made of rubber, surrounding said terminal portion and interposed between said second annular element and a fixed third annular element, and interacting with both,
• said third annular element surrounding said terminal portion and welded thereto,
• wherein said first annular element has, at an internal circumference thereof, an annular guide with a curved internal circumferential surface, said curved internal circumferential surface having, at each point of its circumference, a vertical cross-section with a shape that is concave as it progresses toward an outside of said collar.