Servo U shaped bar

The Servo pen appears to have a reverse lever. However, it is actually a large U shaped bar that is not attached to the barrel at all. The rigid metal U shaped handle runs through a split in the far end of a rigid pressure bar. The bar sits underneath the sac rather than on top. Lifting the “lever” or exposed part of the U bar results in lifting the pressure bar from the back to compress the sac by a pulling type motion.