Hello, I'm about to place an order for a Musikraft Blackguard Neck(1739), and have a question about their options? The list a difference in "Truss Nut" - either "Single Slot" or "Dual Slot". Can someone explain the difference? is it simply the truss rod adjustment at the heel of the neck? One looking like a phillips head screw, and the other like a slotted screw? Thanks for the clarification.