This USA designed aerial has been around since the early 70's and was a top seller before the Springer design arrived.
165cm total length, with a rigid coil (solid, not a spring type) at the bottom and high quality tapered steel whip.
The Thorobred has the same 3/8" fitting as the Springer so will simply screw into any of the standard mounts just the same.
Normal price £11, so to have this aerial instead of the Springer in a package is an additional £1.
You can see more information about the AT-1 / Thorobred Z27 on it's main product page : HERE