I am assuming you have never installed a clutch before. What you are asking about is a clutch alignment tool. It is a tool made from plastic that is identical to the output shaft of the transmission.

As you put the clutch disc, pressure plate up against the flywheel, just start the 6 or 8 bolts, but before tightening them down, push the clutch alignment tool all the way into the flywheel pilot bearing. The trick of this tool is to get a close approximation of alignment between the pressure plate, clutch disc and flywheel before tightening down the pressure plate bolts.

Depending on how good your eye is, will determine how easily your transmission will line up and slide in place.

As for any specs, there are none. It all in the eye.

Bill