Little Giant Jack Screw, 1-1/2 - 2-1/4" (38-57mm) Range, 1" (25mm) Base Diameter. Little Giant Jack Screws are used for leveling work on planer beds, drills, setting up machinery, and general use in toolrooms or machine shops. 191 Series are 1-1/2" to 2-1/4" / 38-57mm in Size. Series 190 and 191 have 20-pitch screws and for those who desire a finer adjustment, the F190 has a 40-pitch screw. Jack Only.