The FZS04 is a 4U Shock mount rack provide the ultimate in protection for sensitive gear as well as heavy loads. Shock Mount Racks provide the ultimate in protection for sensitive gear as well as heavy loads. Each internal rack is surrounded with thick high-density EVA foam and features front and rear rack rails, heavy-duty recessed chrome plated steel hardware and spring-loaded handles, using a 3/8" ply laminate shell.