Assembly for fixing, with fluid connection, a mold bottom to a holder, in which the mold bottom with its main axis is adapted to be demountably fastened to a plate forming an interface between the mold bottom and said holder, said assembly including at least: - a locking device which, operative between the plate and the holder, includes first locking means carried by the holder and complementary second locking means carried at least by the plate, said locking device being able to occupy at least: • a locked state in which the plate is fastened to said holder, and • an unlocked state in which the plate is free to be demounted from or mounted on said holder; and - a fluid connection device which, operative between the plate and the holder, includes at least first connecting means carried by the holder and adapted to cooperate with second connecting means carried by the plate, the fluid connection device being able to occupy at least: • a connected state in which a fluid circuit of the mold bottom is formed by virtue of the fluid connection established between the holder and the plate by said first connecting means assembled with the second connecting means, and • a separated state in which, said first connecting means being separated from the second connecting means, said fluid circuit of the mold bottom is interrupted between the holder and the plate, characterized in that the first locking means and the first connecting means are connected so as to move together by means of a mobile part so as together to form a mobile subassembly. - a locking device which, operative between the plate and the holder, includes first locking means carried by the holder and complementary second locking means carried at least by the plate, said locking device being able to occupy at least: • a locked state in which the plate is fastened to said holder, and • an unlocked state in which the plate is free to be demounted from or mounted on said holder; and • a locked state in which the plate is fastened to said holder, and • an unlocked state in which the plate is free to be demounted from or mounted on said holder; and - a fluid connection device which, operative between the plate and the holder, includes at least first connecting means carried by the holder and adapted to cooperate with second connecting means carried by the plate, the fluid connection device being able to occupy at least: • a connected state in which a fluid circuit of the mold bottom is formed by virtue of the fluid connection established between the holder and the plate by said first connecting means assembled with the second connecting means, and • a separated state in which, said first connecting means being separated from the second connecting means, said fluid circuit of the mold bottom is interrupted between the holder and the plate, • a connected state in which a fluid circuit of the mold bottom is formed by virtue of the fluid connection established between the holder and the plate by said first connecting means assembled with the second connecting means, and • a separated state in which, said first connecting means being separated from the second connecting means, said fluid circuit of the mold bottom is interrupted between the holder and the plate,