These are a replacement for the Alfit / Mepla drawer slides.  The items you came here from are discontinued by the manufacturer.  You get 1 Left and 1 Right.
These are from the same manufacturer BUT these are not "Clip On" as the others are.  These you "Slide On" and tighten the screw on the side.  The smaller screw that is set back is for the up and down adjustment.  These also have plastic dowels that you will need to remove simply by removing the screw and discarding.  Use your old wood screw to attach this bracket on your drawer front. 
Please see link below to be sure you are getting the correct item as there is No Returns on these. 

Mepla Alfit Integra Front Drawer Slide Mounting Brackets