Apparatus and methods associated with an enclosure or structure including two sections that are adapted with a snap-fit interlocking structure. Various embodiments of the enclosure or structures are formed with various case hardening or embrittlement processes to increase embrittlement or hardness of the enclosure or structure so as to create a structure or enclosure which has a desired fragmentation capacity while still maintaining sufficient material properties to permit snap-fit insertion of one section into another section and withstand substantial impacts. Embodiments also provide an interlocking structure that minimizes differences in fragmentation or fracturing capacity as contrasted with other portions of the structure or enclosure. An embodiment of the invention includes an enclosure where one section of the enclosure or structure has a first thickness and the second section has a second thickness, wherein the first and second thicknesses are different. In some embodiments, one section is thinner than another section.