Jdixon86, That depends on the rack you are installing it in. If you have a Dell brand  rack you will need these rails If it is a 3rd party rack then you can find one that matches your rack here - search.dell.com/results.aspx Let me know if this helps.
I know the Dell FS12-NV7 was a custom built server but does anyone know what rail kit will work with these?
FS12-NV7 Rails?