This Discovery tube is 15.5" long with custom-machined holes and slots. It has no caliber indicated, there's only one version for all calibers. All of the holes and slots are perfectly square and line up for a perfect fit. The gauge hole is smaller, similar to the 1701P and Marauder Pistol, so it's stable to mount the gauge without a stock or forearm. This tube is intended for custom PCP carbine and pistol builds.
These have a laser-engraved serial number that may be on either side, top or bottom of the tube. There may be some light scratches from handling during the machining process.