What is the size of the bases that the antenna for the Holybro Moving Base antenna?

ArduCopter Copter 4.4
1

Hello my Arducopter friends I am inquiring to know the base size of the antenna on the Holybro H-RTK Unicore UM982,as I want to make parts to give me about a 310mm spacing on my beloved hexsoon 450,many thanks in advance