Anal- or ass-hook can be an interesting addition for any kind of bondage. Whether it selfbondage or not. It can be worn under or on top of your favoutite fetish clothes (with open or zipped crotch). Can be used to keep you from walking too far or struggling too much.

This is an exerpt from the description:

The way your partner moves when tied determines how the steel ball will move inside of their anus...

There's 5" of insertable length (the ball and a portion of the hook). The hook then rests against the back, while you use the ring (1.5" in diameter) to connect your favorite ropes.
The ball measures 1.5" in diameter and has a 5" circumference. The anal hook weighs .75lbs.

This is another design, without the steel ball. The hook is made out of a hollow polished steel tubing and weighs 1 pound. Measures 12 inches long and 1 inch at the widest point. The insertable portion is 5 inches.

And finally the most simple design - steel anal hanger. It measures 5" in length (the insertable portion is 3" in length). The widest part is .25" in diameter.