Set of 4, using a tube cutter. I suspect these are slightly off-spec from 12mm. Generally, 13mm outer diameter tubes don't exist, so this is based on what I have on hand. These are silicone tubes for replacing the feed and eject rollers of the ScanSnap ix500. Silicone tube: Inner diameter 6.5mm, Outer diameter 13mm, Length 24mm (approximate) These are for replacing the deteriorated roller rubber of the ScanSnap. There are two methods: complete disassembly or partial replacement by making a vertical cut. These can be used as-is for complete disassembly, or by making a cut for partial replacement. Method for complete disassembly replacement: This method involves many steps and cannot be fully described here, so please search online. There is no difference in normal use, and although it takes time, the appearance will be perfect. Method for partial replacement: 1. Remove the feed and eject rollers by making a vertical cut with a cutter and pulling them off. If hydrolysis has progressed, you will need to remove the stickiness with anhydrous ethanol and cotton swabs. 2. Make a vertical cut in the new tube and set it on the shaft of the feed and eject rollers while using the rotation of the power button. I haven't used it, but you may need to use adhesive. If it slips, use adhesive to completely attach it. This is just the surplus I bought personally, so the quality is different from what companies sell. If you are concerned about burrs, please purchase from them. If the quantity is insufficient, a refund will be issued.