Yes,you are right! But what the square hole?

 

My best guess for the square hole is for machines to grasp during production. I doubt, but it could also be for access for something inside during production.

But like I stated earlier in this thread, you can tap the sleeves and thread a bolt to mount a hi lift very securely and inexpensively

 

I have a small bee nest in that hole, spayed the shit outta of it with raid