If your Specialized mountain bike is of the past few model years all the way up to the current then your bike takes an IS 42/28.6| IS 52/40 headset. We make that in our 40 Series (BAA0783K) our Hellbender 70 Series (BAA1189K) and our 110 Series (BAA0841K).
One other thing to note is that your Specialized mountain bike will require an extra step to work with our headsets. Due to Specialized's use of a deeper headtube bore depth than Cane Creek headsets were optimally deigned for you will need to use Micro Shims to accommodate for this difference. Those Micro Shims can be purchased through our Webstore in .25mm, .50mm, and 1.25mm widths. It helps to have a couple of each on hand because the required amount seems to vary from bike to bike. You will need in the range of 1-4mm worth.
For a description on how to install these Shims refer to this article.