Abstract: A collar for a telescopic cylinder with a cap includes the terminal portion of the cap that presents the opening of the cap, such that the collar includes in the following order a first annular element with a contoured profile, which surrounds the terminal portion and is welded thereto, and a second annular element, which can move with respect to the terminal portion and to the first annular element. The collar further includes an O-ring, made of rubber, surrounding the terminal portion and a third annular element surrounding the terminal portion and welded thereto. The first annular element has, at its internal circumference, an annular guide with a curved internal circumferential surface, the internal circumferential surface having, at each point of its circumference, a vertical cross-section with a shape that is concave as it progresses toward the outside of the collar.