Hi,
The 9x4 and 10x4, 11x4,12x4 on this is the same as apc... the inner hole is 6mm and can be bore out to 8... the OD is 12.60, so if you bore out to 8, you should have 2mm left each side, The top is pretty much flat...
Here, I attached some pictures.
PS: I am sorry about the mistake, I didn't realize the DJI one need 8mm. (but if it work, I don't mind on boring it to 8mm if request)