The anus can draw objects inward, and a toy that ends up completely inside can be difficult to get out. Everything used anally therefore needs something that stays outside the body: a flared base, a wide handle, or—on chains—a sturdy loop.
A loop is not a base. It doesn’t prevent the chain from sliding in on its own; it only lets you hold it and pull it out. Therefore, a simple rule applies for ball chains with a loop: the loop must always be outside the body and within reach, and the chain should never be left without supervision. Never insert the entire chain.
Also check how the loop is secured. Chains like Mr. Play and Blush Anal Adventures are molded in one piece of silicone, without seams between the balls, the stem, and the loop. That means there are no weak joints and no gaps where dirt can collect. Balls threaded on a string can’t be made completely clean or controlled as easily.
If you want a toy that can stay in place on its own, choose one with a wide base: Anal Fantasy has a wide, crosswise T-base, and Lelo Soraya Beads has a broad handle that works both as a stop and as a grip.