check out page 32 and page 40 of this PDF
http://us.allegion.com/irstdocs/manual/108482.pdfI think you'll get all the details as far as door thickness, Primus Classic or Everest Primus, or the new Primus XP, tailpiece model, and plug and shell model numbers which all together tell the Allegion (they own Schlage these days) rep what deadbolt you are trying to buy.
CP keyway is Classic Primus by the way... and Robotnik is right about the C100, C123, C145 convention for Everest Primus, but other keyways exist.
I'm not a Primus expert, so this info may not be 100% Calling an Allegion regional rep may also give you the answer, your locksmith should honestly have their number in his rolodex.
Squelchtone
EDIT: looking at page 9 on this PDF catalog
http://www.locksmithingeducation.com/Sc ... l_2007.pdf I am beginning to understand their literature.. Classic Primus is pretty much on its way out, it seems this whole catalog caters more to Primus Everest, so the part numbers listing Conventional or Primus should more clearly say Conventional Everest, or Primus Everest.
If that's the case, If you are looking for Primus Everest B700 series deadbolt, then it looks like a B762 for a 1-3/8" to 2" door is cylinder 20-745 and for the thicker door of 2"-2-1/2" the cylinder is 20-746 after you decide which one you need, the lock will arrive in whatever Everest Primus keyway Allegion decides to sell to your locksmith, and if he's not a regular Primus dealer, it will probably be some nationally available keyway section like C123 or C145