MIL STD- Metric System Application in New Design

5.1 Metric units
Metric units, practices, and usages shall be in accordance with ASTM E 380 and IEEE 268

5.1.1 Preferred units
Unless otherwise specified, the preferred metric units for the commonly-used quantities shall be in accordance with FED-STD-376

5.2 New design
New items designed under contract shall be of metric design. Hybrid design, however, is acceptable where required to accommodate existing customary items selected in accordance with 5.3. Where applicable U.S. Government, non-Government (adopted for use by DoD), U.S. National or international documents exist which establish preferred metric modular sizes or other design standards, they shall be used to the maximum practical extent, where a U.S. standards is established with greater definition or restriction than a prevailing international standard, the U.S. standard shall apply.