/ Precision Measuring Tools / Precision Hand Tools / Precision Shop Tools / Jack Screws / 191F * Not actual product image 50693 191F Little Giant Jack Screw- Extension V Base Only 50693 Other similar products 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. Extension V Base Only. Contact Starrett