Looks like he is using a "ruling pen" used to ink in the straight lines around the border of the engineering drawing and its title block. It also appears that he is getting the paint thin enough that it flows through the ruling pen making a consistent line. Experience pinstriping with a brush says that if you get the striping material too thin it will spread out to make a wider line which will not be the same width or weight as it is wicked out to the surrounding painted finish. I have attempted to "micro-stripe" using a fine ink pen the kind made by Speedball, JB Hunt with some success in the past. Make sure that you use an extremely light hand on the pen otherwise you will dig right into the paint causing the striping paint to flow into the scratch. Long straight lines take the highest degree of skill to pull.
What I finally ended up using was a trimmed watercolor type "Rigger" brush, the type brush used by watercolor painters for fine lines and ships rigging, hence the name rigger. A 2/0 or 3/0 rigger brush will still need some trimming from the ferrule end of the brush. While the brush will produce the most consistent line, the ink pen will take the least amount of practice and skill.
Also if you are going to use a clearcoat over the stripes you can get away using a waterbased paint acrylic or even a poster type ink. Enamel while it is the paint used by many stripers can be clear coated requires light mist coats to keep it from spreading or you can leave the striping right on the topcoat without clearcoat.
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