These strap extenders are most commonly used to extend the straps on armor that is to tight or elongate straps that are a bit short, simply make sure the strap widths are the same and then attach one extender per strap put your item on and your ready to go.
 
Brown leather with antique brass buckle or black leather with nickle plated buckle.
Buckle - 3 cm wide.
Strap width - 2.5 cm.