Solved How can I add a slot for my trucks cab to go on the frame?

Hello, so I'm fairly new to making cars and puttin them into the game, but yesterday I was trying to figure out how to make it so there would be a new slot under the frame slot in the parts selector but nothing worked, could someone tell me how I can make a new slot show up?

 

.... then how is it that the d-series has a slot for the body under the frames slot

 

So, but i just needa know how to make a slot for it.

 

If this is still unsolved as the tag says, a slot wont show up until you have a part that can go in it, so you will have to make the body or at least a placeholder part to test the slot.

 

oooooooooooo ok, makes sense