When you buy Refurbished sieve columns from Oxus, you are buying quality product from an FDA Registered, ISO 13485 Certified OEM Manufacturer in business for over 20 years. Our Inogen One G3 Replacement Sieve Columns are FDA Cleared. We can offer you lower pricing based upon your return of the used sieve column “cores” you are replacing. Oxus makes this easy for you by providing free 2-Day shipping to you (shipping available to the US only) and a pre-paid USPS return envelope to return your cores back to Oxus in. Once you have received your order and followed the included Oxus Column Change Procedure to remove your used sieve columns and install your new Oxus Refurbished Sieve Columns, all you have to do is place your used sieve columns and blue service tool back into the box they came in and place into the included USPS return envelope and into your mailbox.