A substrate-mountable holder system, comprising a base having a hook, a first front surface and a second front surface with a groove therebetween, wherein the groove includes a rearward facing face having a step. The system also includes a second portion for operatively engaging the first portion, the second portion including a tongue component positionable within the groove, wherein the tongue component includes a forward facing face having a step. The base also may include at least one notch extending inward from the rear surface, the notch having a first surface at a first depth relative to a rear surface of the base and a second surface at a second, deeper depth relative to the rear surface, and the cover may have at least one ear for releasably engaging the at least one notch.