There is a split.
Do you know the actual size of the ball joint? Can't seem to find the size of the sockets in any of the details.
I have a forum post to create about ball joints – but only 8 months behind on writing it.
A 2” open end wrench will work but an crescent wrench works best – if you don’t have the socket.
Actually, both work great, together.
Edit: be very careful when screwing in a ball joint, regardless on which tool you use – for it is easy to get one cross-threaded/joint going in at an angle. Take your time for if you get one on at an angle/cross-threaded, then you will not be able to re-use that arm (hole stretched out).
Depending on who you talk to, you "might" be OK by using the arm with a cross-threaded/angled ball joint (my opinion is NO, don't use it) – but it is best to just do it correct the first time.
The ball joint top has 4 square edges with rounded corners, something like this:
Separate names with a comma.