Usually there is a tool available for this purpose. If not, it should be made. It is a quick lathe job on a piece of plastic or aluminum.
the input shaft has splines on it which connect to the clutch friction plate.
front transmition shaft Input Shaft
From the engine, there is the clutch shaft which drives/or connected to the Input shaft, which in turn drives the output shaft.
Transmission Input Shaft
The input shaft of the transmission.
If you are asking what a clutch shaft is related to the installation of a clutch, it is a plastic alignment shaft that is used to line the clutch disc up with the pilot bearing in the flywheel, so that when you install the transmission the transmission input shaft will slide thru the clutch splines and into the pilot bearing in the flywheel with relative ease. They are a must for any clutch installation!
Transmission Input Shaft
Transmission Input Shaft
The bearing lets the belt pully free wheel on the compressor input shaft that the clutch is attached to.
A spigot shaft is also known as a primary shaft or an input shaft in an automotive gearbox. It protrudes from the gearbox into the bell housing and connects the clutch plate to the transmission.
It is on the input shaft of the transmission (inside the bellhousing). to remove it you need to remove the transmission enough to slide the input shaft, remove the hydraulic lines that control it and slide it off the shaft.
It will be due to the input shaft bearing in gearbox.