Your Scuba Pro X-TEK System uses Bolts to attach a Variety-of-Accessory-Item to the System. The Single Tank Adapter and Soft Back Plate use these Bolts. The Back-Plate (Aluminum or Stainless Steel) have Multiple Holes for attachment of other accessories to X-TEK Harness. Having Spare Bolts available for Replacements or when adding Accessory Items makes good sense. Always Carry some Spares in your Save-a-Dive Kit. Bolts are made from Corrosion Resistant Stainless Steel and come in 14mm and 9mm (0.55" and 0.35") Sizes depending on your needs. Bolts are covered by a 12 month limited warranty.