Also known as adel clamps, these nifty little clamps are great for attaching all sorts of stuff to your bike.
They can be used to mount quarter fairings or number plates to your handlebars or fork tubes, belly pans or lower fairing mounts to the lower frame tubes, vintage seats to seat rails and all sorts of other hardware like puke tanks, electrical panels, undertrays etc. etc.
Stainless steel, 1/4" hole.
Sold each, available in six diameters: