Abstract: A socket cavity formed in a concrete slab of the type poured horizontally and subsequently tilted up, which cavity affords engagement of hoisting equipment to the slab. The inner portion of the cavity is in the form of a frusto-conical wall surface communicating with the surface of the cavity through a cylindrical bore concentric with the frusto-conical surface. The cavity is formed by placing in the slab form an expendable flask-like hollow article formed of synthetic resin or the like which is left in the slab after erection thereof. Engaging apparatus cooperable with the cavity which has on the inner end thereof arms that are pivotally moveable between a retracted position and an extended position, the arms engaging the frustoconical wall of the cavity when in the extended position.