Hi Gregg,
Following up on what Jerry said, the lines are called a "thick and thin" border. One line is heavy, the other is light and thin. There are gravers that cut multiple lines but the resulting lines tend to be light because you are removing a lot of metal if the graver goes deep. Usually liners are used for background shading. I suspect the lines on the lock were cut with single line tools with one line becoming the visual guide for the second parallel line. It is not that hard to do with practice. It is harder on that curved lock plate surface because you really have to make sure your graver is perpendicular to the surface. If tilted because of the curved surface, your line will vary in width. Kutter, who posts on this forum, mentioned that he uses a thin flat grave for the thick line. That way you tend not to tilt the tool over and even if your cutting depth is a little uneven, the line will not widen as it will with a square graver.
dave