This is a 3/4" bore master, commonly used for front disc brake cars.
Installation note: When removing and installing the master, it's strongly recommended to use a crow foot wrench since the lines are in such tight quarters. It's very difficult to get a tight seat when trying to use a traditional wrench.
Installer's Note 2: Check the length of your push rods before installing the new master cylinder. 2 different lengths of push rods were used depending on the size of the bore of the master and it's impossible to know who has installed what over the years. The correct push rod length for the 3/4" bore masters is about 3-11/16". These are shorter than the 7/8'' bore push rods; we do NOT have the shorter rods available, so if you have the longer rods and find there is not enough play when adjusted in you may have to shorten the ones you have.