Abstract: A mold assembly for injection molding including a female mold having a first pair of opposite inside walls and a second pair of opposite inside walls disposed at four sides and defining a trapezoidal cavitys two trapezoidal locating plates respectively fastened to the first pair of opposite inside walls inside the female mold, and defining two symmetrical pairs of sliding ways within the female mold at different elevations between the trapezoidal locating plates and the second pair of opposite inside walls, and a mold set fitting the trapezoidal cavity of the mold set, the female mold consisting of a left mold half and a right mold half detachably abutted together, each mold half having two sliding tongues at different elevations and slidably fitted into the sliding ways.