Brake Fluid Reservior Problem...

[Flash]

I can't seem to take my cap off my brake fluid reservior. Is it supposed to be hard to take off? It seems like there's a flat side on my cap. But I was looking at another picture of a 2g's brake fluid reservior and it appears to be flat on one side too! Right above the teal circle, is the flat part I'm talking about.
How do I take the cap off?

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[ECLIPSE4x4]

Never saw one with a flat spot.

They usually just thread off.

 

[Flash]

Well I went and got a tool that is better then a hand and I got it off! So tomorrow the big brakes go on. It was even tough with the tool to twist it off.
Thanks!