Definitions for "slip clutch"
a friction clutch that will slip when the torque is too great
A safety device usually located on the focus knob allowing the knob to "slip" and continue turning when it reaches the end of its travel, or if it runs into the stage. Due to the gear ratios involved, without this it may be possible to damage the mechanism by applying too much force to the knob after it has reached the end.
When students bring the focus all the way up or down and continue to try turning the knob, damage to the focusing system can occur if there wasn't a slip clutch. This mechanism is one more extra thing we make sure is on every microscope we sell.