Building wearables for kitties?

[Thorn Witrial]

Good morning, folks.

I know how to make things. My question is how do you make things that are wearable by kittycats?

For example, the collars. You set a bought collar box by the kitty, click on it, and it attaches, right? (I don't know, I've never bought one).

I want to make other things for kitties to wear but I don't know how to make them an officially useful to kittycats product like the collars are.

Halp?