Yes, I would recommend the 6" grip ruler from Accents in Design made in Usk, WA. This is my go to ruler for most everything, especially cross hatch work. She has a set that is even better because it has a couple different sizes for curves and one of them works perfect for clam shells. They have etched lines that help you keep lined up. Her rulers are called Fine Line Rulers.
http://www.accentsindesign.com/fineline.html Check it out.