The CP02FP is designed to center a FiberPort inside a 30 mm cage system. ER rods can be inserted into the four holes provided in the adapter as shown in the boxed image above. In addition, the four #2-56 stainless steel socket head screws necessary to secure a FiberPort to the adapter are included, each of which is 1/4" long. CP02FP has internal SM1 threading, enabling it to be used with our extensive line of lens tubes.