The apparatus includes a base having a hole in a top surface, a fastener having a longitudinal section with the longitudinal section extending into the hole, and a shell. The shell has a connecting section connecting a first lateral surface section and a second lateral surface section. At least a portion of the first lateral surface section extends into the hole. The second lateral surface section extends away from the top surface of the base. The connecting section is disposed between the top surface of the base and a portion of the fastener. The connecting section has a first section and a second section, and the first section has a non-linear cross-section. The apparatus further includes a washer disposed between the portion of the fastener and the connecting section, and a portion of the washer engages the first section of the connecting section.