This is a safety mechanism for https://makerworld.com/en/models/172691#profileId-200960 this pill container. The mechanism works really well and I just felt it needed something to both cover the pill hole as well as keep the mechanism being triggered by pets or children. This fits in snug with a snap. Once its in its hard to get out with your fingers by design. In order to release it enough to free it you push the mechanism half way. This causes the drum to add some pressure to the internal bar and allow you to pry it free. Don't push too hard or you might break your spring. This is not a perfect solution for that reason so please use with some caution. This is for the v3 version. Though as long as the hole sizing doesn't vary it should work with the other version.