From the product description, check product page for current description, price and availability:

• Food Grade 2 Micron Diffusion Stone with 304 Stainless Steel 1/4″ Barb, High Qulity and Anti-Corrosion;
• Durable Construction:Food Grade Stainless Steel Materail, Guarantee No Rust or Leak;
• Various Use, Best Choice for Oxygenation and Carbonation, for Beer, Soda, or Coffee;
• 3-5 PSI is the best Work Pressure for the Diffusion Stone;
• Quality Guarantee: Any Defective for Diffusion Stone, Backed by 45 days Money-Back.