Instead of keeping an assortment of parallels on hand, adjust these two-piece tools to your exact height requirements. Loosen the screw and slide the pieces in and out. When the desired height is achieved, tighten the screw. Parallels are precision ground on the top and bottom edges and are often used in pairs. Place a parallel against each vise jaw and rest your workpiece on top to raise it within the vise and allow more clearance for cutting tools.