Abstract: The disclosure is directed to a device for forming a post-receiving cavity in a solid material during the solidification thereof with the device including a clamping element having first and second side walls disposed in facing relationship to each other, with each of the side walls having a vertical extent, and a resilient wall which extends between the first and second side walls and interconnects the first and second side walls intermediate the respective vertical extent of each side wall to thereby divide each side wall into an upper end portion and a lower basal portion. The resilient wall is constructed and configured to cause the upper end portions of the side walls to move outwardly in response to application of an inward lateral force to the lower basal portions of the side walls and also to cause the upper end portions of the side walls to be maintained at a predetermined distance from each other in the absence of any inward lateral force being applied to the lower basal portions.