This is the button-hook.

Most of these hooks mounted on sweatpants, as an independent hook and paired with a button. I.e. if the wide belt that often install and button and hook. It all depends on the imagination of the designer.                               

The dimensions of the main parts:

The Production Of China.

  The hook 10 x 12mm, bottom hole Ø 4 mm, the upper hole Ø 6mm                                  
  Plate 9 x 12 mm, bottom hole Ø 3 mm, the upper hole Ø 6 mm.

(Weak metal)

The Production Of Turkey.

  The hook 9 x 14 mm, bottom hole Ø 3.5 mm, the upper hole Ø 6 mm
  Plate 11 x 14mm, hole Ø 3.5 mm.

(Metal is more durable)

They are two types of hooks that are most often used.

As the front part, you can apply any facial portion of the button, just like the customer. 
You should pay attention only to the diameter of the cylindrical part of the button, what would it compatible with the diameter of the hole of the hook.

(The smaller hole of the hook is designed for mounting the cylindrical part of the button, the larger the hole for the nozzle)

If the cylindrical portion of the button is more necessary length - make it shorter.     

To be continued: