Kesteb,
Thanks for the reply.
I figured that was the purpose on the older style which had the piston retainer to retain the boot.
If it is really needed, does anyone know if there is a different boot and retaining method i could use?
I really do not want to drill holes in a new master cylinder fro the metal retainer.
The attached photos show a master cylinder the same as I have now in which the user drilled two holes and used the old retainer and boot.