8' Aluminum Lok Rail for Side-Roll Kits. This aluminum Lok rail is bolted to the driver side of the trailer and is used in place of ratchet hold downs. The Lok rail runs the entire length of the trailer and adds much more support and locking force than a ratchet hold down. This method of securing the tarp is much faster than a ratchet style. The tarp pocket and roll bar are secured under the Lok rail by the operator turning the crank handle and locking the handle under tension.