an insert comprising a body to be embedded in concrete and having a prong smaller in size than said body , connected at one end to said body by a frangible neck . the prong has external ridges and is adapted to be driven by a hammer into an undersized opening in a mold to securely mount the insert in place . after the concrete has set , the prong is automatically broken off , i . e ., separated from the embedded portion of the insert , as an incident to the stripping of the mold from the work .