Two half hitches is an easy knot used to join a rope to a pole or a log when you are not concerned with it staying tight. It is adequate for tightening ropes from a tent or shelter with stakes. As long as the knot stays under a constant load (that is, an unchanging amount of pressure) it shouldn't budge. If you are tying it around a slick surface (such as a metal pole) or a thin stick, the knot will be more effective if you first tie a roundturn (loop crossing over) before tying the knot. Otherwise, the knot will just spin around the object and could break into a different knot. Many boating books teach that a roundturn and tightened two-half hitches is an ideal knot for mooring a boat to a dock.
How to Tie Two Half Hitches:
Begin by forming a clockwise loop around the pole, with the working end of the rope on top. Bring the working end through the loop. At this point, you have an overhand knot around the pole.
Bring the working end down and to the left. Loop it over the standing end. Pull the working end through the loop just formed and tighten the knot.
For a video of tying Two Half Hitches with a Roundturn, click HERE.