Pivot hinge with fine adjustment for vertical on the pin.

[jdaley]

Close here is a photo, plummer blocks are cast iron units into which a bearing is inserted. The bearing can move a bit to self align in the block.
You may notice on the square tube column rising from the bench or even the first 'knuckle', a bolt head on one side and at 90 degrees another bolt head higher up the sq tube.
They are the adjustments. A single bolt right through at those 2 positions.