MIL STD- Military Specifications and Associated Documents, Preparation Of

4.4 Part or Identifying Number (PIN)
When a military specification covers more than one part, item, or material that is subject to assignment of National Stock Numbers and an identification problem in the Federal Supply System may results, a specification-based PIN to identify the parts, items, or materials shall be included. If a PIN is need, its construction shall be provided by the DoD activity requiring it. PIN's shall be kept short and shall not exceed 15 characters. If it is considered that such a limitation cannot be adhered to, a proposed deviation with detailed justification shall be submitted through the DepSO to DPSO for approval.