When sourcing metal magnetic stripe cards, you must prioritize material grade, typically 304 or 316L stainless steel, to ensure corrosion resistance and durability. The card thickness should ideally be 0.8mm to 1.0mm to ensure compatibility with standard POS terminals and ATMs. Furthermore, the magnetic stripe type (HiCo 2750 Oe vs. LoCo 300 Oe) must be specified; High Coercivity (HiCo) is recommended for financial and access control applications due to its higher resistance to accidental erasure.