Somewhere on your Thermaltake case, it will say the model of the case. We will need that model. Alternatively, you can browse through
http://www.thermaltakeusa.com/chassis.aspx website till you find the case that looks like yours. How old is your case?
With my Thermaltake case, there was no model name or number on it. I had to go through each of the options on the side of their web page to find it. For example mine ended up being a Mid Tower V series:
http://www.thermaltakeusa.com/Chassis/Mid_Tower_With_Power_/V_Series/C_00001578/V3_Black_Edition/design.htm