Welcome.
You need to look on the bottom of your master. The bore diameter will be stamped. Memory tells me it should be 13 mm, but I'm not positive.
Then go to this page...
https://store.bevelheaven.com/Rebuild-Kits-Parts/ ...scroll down, and pick the hollow pivot kit that corresponds to the size you need. If you're not in the US the Brembo part# is listed so you can find it closer to your location.