I don't know what the video courses say, but you don't checker that strap as you do wood, one line at a time. Assuming you don't have a checkering cutter and a milling machine, you use a checkering file, which cuts a number of lines at one time. They are available in 20 lpi to 75 lpi. Like any checkering, practice first on scrap metal. Brownells has the tools and also a video guide.
Jim
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