Help With Mainspring Arbor

[jab123]

I'm fairly new to this hobby. I just ran into a mainspring arbor that is in three pieces.  The part that hooks to the spring is held to the shaft of the arbor by a pin. How do you replace it once the mainspring is replaced?

 

Thank You

[Geo]

Welcome to the forum Jab123. I personally haven't seen a three piece arbour, pictures are always a good idea along with the complete movement to let folk know exactly what it is you have.