The Lockstack™ D03 retaining system includes stacking fasteners that eliminate the need to size and cut thread stock for D03 sandwich stack assemblies. The system also includes a novel isolation retainer that engages the fastener heads to resist loosening during disassembly of the directional control valve or other stack component(s) above. Use the Lockstack™ system to reduce labor costs and sandwich assembly headaches, while adding value and integrity to your sandwich assembly.