The Titleist Pro V1x is a variant on the standard Pro V1. The Titleist Pro V1x was introduces as a harder feeling ball than the Pro V1 golf ball and with a 4 piece construction as opposed to a 3 piece construction for the Pro V1. It was designed to spin less than the Pro V1. In 2007, Titleist introduced the Pro V1 and Pro V1x with a putting stripe. For more info, see the page at Titleist Pro V1.