Edge Detection from Mouse?

I need to detect and edge of a part from the mouse position, how would I go about doing that exactly, here is a reference image.

https://media.discordapp.net/attachments/837811540563329054/849113227748966431/5ca5a4db7e28e0990bf5fed1cf262f9b9fb79d8e.png?width=822&height=612

What you could do is add a part and size it so that it follows the edge, and then just check if the mouse is close to that.