What it is
What STANAG 3212 covers
STANAG 3212 is a NATO standardization agreement, not a technical specification in its own right. Its interoperability requirement is to establish a minimum and/or maximum size of orifice for the gravity filling point of the aircraft tank or reservoir relative to each fluid, and a minimum and/or maximum size for the external diameters of nozzles used for the gravity filling of aircraft with fuel or other fluids. The actual figures are not in this document. Participating nations agree that internal diameters of orifices used for the gravity filling of aircraft "shall be in accordance with Table 1 of ISO 102", that external diameters of fuelling nozzles "shall be in accordance with Table 2 of ISO 102", and that nozzles used for other fluids must still fit the relevant minimum orifice diameter given in Table 1. ISO 102:1990 (Aircraft - Gravity Filling Orifices) carries those tables; STANAG 3212 is the NATO agreement that makes following them a national commitment.
This is Edition 7, promulgated 23 May 2017, which supersedes Edition 6 of STANAG 3212.
How it binds
A STANAG does not bind a supplier by existing. It binds a nation once that nation has ratified it, and a nation treats it as implemented once it has issued instructions that all future aircraft will be in accordance with this agreement - new aircraft going forward, not a retrofit of an existing fleet. Partner nations are separately invited to adopt it, without a ratification obligation. Nations record their ratification and implementation position in the NATO Standardization Document Database, and may report on it using the forms in Annex H (for members) or Annex G (for partners) to AAP-03 - a reporting mechanism, not a technical requirement of the STANAG itself.
For a supplier or manufacturer, the document does not create an obligation on its own. It becomes relevant once a contract, a tender, or a national requirement calls up STANAG 3212 or ISO 102:1990 directly for a given aircraft or fuel-system component.
What it does not cover
The STANAG names no other related document beyond ISO 102:1990 for its technical content - the "OTHER RELATED DOCUMENTS" section reads "None." It says nothing about fuel or fluid quality, fuelling procedure, or the rest of an aircraft's fuel system; it covers the size of the gravity filling orifice and the fuelling nozzle only. It carries no in-service or maintenance obligation, and it does not describe what should happen to an aircraft already built before a nation's implementing instruction takes effect.
Review
The STANAG is reviewed at least once every three years, with the result recorded in the NSDD, and nations or NATO bodies can propose changes at any time. The tasking authority for this STANAG is the Military Committee's air standardization body, MCASB.