On Sat, 23 Sep 2017 14:47:08 +0000, Stormin' Norman
wrote:

The splines on the clutch disc must line up with the splines on the
flywheel.

When the pressure plate is tightened in place, the clutch disc is held
very firmly in place. Without aligning the splines first, you will
likely have a very difficult time inserting the transmission shaft
through the clutch disc and into the flywheel.

Most DIYs seem to gloss over this step.

As an example, this DIY at time 331 seconds, simply shows the bright red
centering tool already in place!
https://youtu.be/S5xSOy03NAg?t=331

That same video, shows at time 352 seconds, a *different* centering tool.
https://youtu.be/S5xSOy03NAg?t=352