A pilot bearing puller is a specialty tool used during clutch replacements on manual transmission cars. The pilot bearing is located in the center of the engine's crankshaft flange and supports the tip of the transmission input shaft. Because it is pressed into a blind hole (a hole with a closed back), a standard puller cannot get behind the bearing. The pilot bearing puller uses expanding jaw fingers to insert through the bearing's center hole, expanding to grab the back edge of the inner race.
Once the jaws are locked in place, you tighten a slide hammer or a bridge screw against the tool. This pulls the bearing straight out of the crankshaft recess. Using make-shift tools or a hammer can damage the soft brass or needle rollers, leaving metal shards stuck in the crank. Standard alternatives like the hydraulic bread trick (packing the hole with bread or grease and hammering a bolt in) are messy and can fail on rusted bearings.