suspension thread size

[powey]

What is the size of the rear suspension thread ( the one in the boot under the rubber cover ), as im currently making a strut brace

 

[powey]

The pipe is cut to 40"
Had to cut 2 disks to weld on either end as the pipe is hollow. Then turned the disks and welds down on a pedestal grinder
Tomorrows task is to weld a flange either end with a hole in it to mount to the supsension tops

 

[powey]

Anyone in the know?