Micro-registration systems enable the printer to fine-tune the screen registration after the screen has been lined up and clamped in place. These systems move the screen in either the X or Y direction or a combination of both. Micro-adjust systems come in all sizes and shapes. Some are attachments to an existing press that are precision-made pieces, while others are simply screws that apply pressure to the screen frame and push it into place.
A good micro-registration system can save countless hours of frustration in lining screens up and keeping them registered.
Source: "Encyclopedia of Garment Printing"