Video- that shows a complete installation of the large shaft.
Remove the collette nut 
Remove the 4 phillips head screws that hold the front assembly on 
Remove the front assembly 
Unscrew the Phillips head screw inside the black cylinder 
Unscrew the Black nut on the front of the die grinder. Note- This is a reverse thread! Hold the neck with a vice. You will get scratches from the vice on the neck. Now mail us the front assembly 
Now the next step is a bit tricky. If you don’t have an Arbor press send the front assembly to us & we can do this step for you. Press out the stock shaft. & press the new shaft back in. We will send the neck back after this step. 
Place the black cylinder over shaft 
Tighten the small Phillips head screw inside the black cylinder 
Reattach the front assembly using the 4 screws 
tighten the Black nut on the front of the die grinder. Note- This is a reverse thread! You are done