Clutch Disc Alignment Tool
A clutch kit typically contains a plastic clutch alignment tool. It has the same dimensions as the transmission's input shaft. It has splines that match the splines on the clutch disc and a pilot that fits into the pilot bearing. It aligns the clutch disc to the flywheel and the pressure plate before torquing the pressure plate's cover.
The clutch pilot bearing is a ball or roller bearing or a brass bushing that centers the transmission's input shaft in the crankshaft flange. After assembling the clutch disc and pressure plate to the flywheel, slide the clutch alignment tool through the pressure plate's diaphragm, and the clutch disc's splines into the pilot bearing.
Remove and replace the pressure plate's bolts according to specifications in a criss-cross pattern. Make sure the tool and clutch disc is centered while torquing the bolts. Ideally, the transmission input shaft will slide right through the clutch splines, and into the pilot bearing, but it usually takes a bit of wiggling around to get it aligned and then the transmission aligned with the engine.