Bathroom sink pop-ups are raised and lowered with a lift knob or lever, usually located on or near the faucet body. The knob or lever is connected to a lift rod that is fastened in many cases to a flat, slotted bar called a “clevis.”
The flat, slotted clevis is connected by a small spring clip to a pivot rod–and–ball assembly—a rod that runs through a rubber pivot ball and slopes slightly upward to the tailpiece of the stopper. This rod pushes the stopper up or lets it drop down into the drain body.
The lever operates a lift linkage that pulls on a spring. The spring pulls a rocker arm that raises and lowers the stopper (see the illustration).