An adapter for releasably securing an assembly, such as a parking meter, to the top of a hollow post and including a resilient member having a tapered bore formed therein. The resilient member is inserted over a complementary tapered base member extending from the lower surface of the assembly. A nut is threaded onto the lower end of a bolt which extends through the base member for retaining the resilient member thereon. The periphery of the nut is shaped so as to non-rotatably engage with the inner surface of the hollow post upon which the assembly is to be mounted. The nut, the resilient member, the tapered member, and the bolt extending from the lower surface of the assembly are inserted into the post and the bolt rotated so as to screw the nut onto the bolt, compressing the resilient member to wedge it onto the tapered base member, causing the resilient member to expand between the base member and the inner surface of the post so as to fixedly secure the assembly onto the post. The base member and the bore in the resilient member are frusto-conical in one modification and substantially pyramidal in another.