What is it? Gold thing on this master cyl

I have to say thanks guys. This little thing has been crawling around the back of my mind for the last few weeks. I've been around cars for a long time but have never seen anything like this...well at least not on brake lines. It appears to be similar to a clutch fluid damper system.
Don't worry, I'm not going to add them, it just was killing me not knowing for sure what it was. I will say that the brakes in my car seem to have more "feeling" to them, kinda like the manual disc setup on the Duster vs a power brake system that always feels "soft" to me.