The disposable assembly has a closed body, for containing a first component and having a lateral surface, a bottom and an upper opening. The bottom has a mounting projection extending within the body for its sealed interlocking engagement in the complementary conformation of the lower end of a hollow inner tubular member intended to contain a second component while its other end is closed by a sealing means. A shutter is tightly mounted on the opening of the body using screws, or by clipping or interlocking. The shutter and the sealing means or the shutter and the hollow tubular element can be a single piece. The presently described embodiments are suitable for producers of paint, varnishes, primers and other products to be sprayed or projected using a gun and other manufacturers of spray or paint guns.