Buntline Hitch

Use this knot to fasten items such as snaps, towing eyes, and rings to rope or cord. It forms a small, neat and reliable knot. It is a secure knot, but it tends to jam, so it is not easy to untie. It is useful for work that will be left unattended for longer periods, since it will not untie suddenly. This knot should not be used for tying to a climbing rope however.

To Tie a Buntline Hitch:

Pass the end of the rope through the shackle then back up across the standing part. Make a turn around the standing line, forming a loop with the shackle at the base of the loop.
Bring free end across tops of both parts of the loop. Make a turn around the standing part of the loop, making sure free and exits between itself and the standing part of the loop.
Pull the knot tight down onto the shackle.