There are two kinds of slant buttonholers. One is the 'professional' - it works with zz slant machines and you use the zz settings from the machine. The other works with the 301 and 404 as well as the zz slant machines and the zz settings are on the buttonholer.
The circular stitcher will work with the 301 - it just will sew circles or half circles. If you use it with a zz or decorative stitch machine it will do cooler looking circles or half circles
directions should be on line somewhere.