There isn’t a gauge for this as it isn’t made to fit anything. It can be bigger or smaller depending on the yarn weight you choose but I made this from a DK weight yarn with a 4.0mm hook.

I haven’t included any real instructions on how to attach the bobby pin but it’s just sewn onto the back, there is an image showing you where I attached it. Anything will work though to attach it to your hair or you can choose to not sew the bobby pin on but just use them to attach to your hair when you want to and then keep it as a squishy toy for the rest of the time. :)