Black = actuator
Blue = shifting block. The shifting block houses a bearing and a shaft that connects to your dog gear. The dog has a steel cotter pin going through it that allows it to slide back and forth in the slot in the hex shaft. The dog engages and disengages the drive sprocket (or whatever you're trying to shift).
http://ep.yimg.com/ca/I/yhst-3383317..._2090_36957746
http://ep.yimg.com/ca/I/yhst-33833170891817_2090_641582
That is the shifting block. On the other side is a drilled and tapped hole for your actuator. The shaft that you see has a through hole at the end for the cotter pin.
Hope that helps.