What are the two variations of the square knot to avoid for rigging purposes?

The two variations of the square knot that should be avoided for rigging purposes are the Grief Knot and the Thief Knot. The Grief Knot is known for its instability and tendency to slip, making it unsafe for securing loads under tension. This knot is unreliable because it can easily come undone when subjected to lateral forces.

Similarly, the Thief Knot is also dangerous for rigging because it can slip and does not hold reliably under load. This knot is essentially a variation of the square knot that doesn't provide the same uniform tightness and security as more reliable knots used in rigging, such as the bowline. For safe rigging practices, it is crucial to use knots that maintain their integrity and do not have a high likelihood of coming undone when loads are applied. Therefore, avoiding both the Grief and Thief knots is essential for ensuring safety and stability in rigging applications.