Which direction does the concave surface of the slingshot tie rubber band face?

When tying the rubber band, prepare the rubber band first, put hemostatic forceps into the leather bag, use a small tie to put hemostatic forceps through the leather bag, and use hemostatic forceps to clamp the rubber band. Pull the rubber band from the hole of the rubber band, and the rubber bands are aligned, so that the unbuttoned end of the rubber band differs from the tied rubber band by one rubber band thickness. Hold the head of the rubber band with your thumb and forefinger, press the head of the rubber band together and tighten it, and fix the bag on the nail. You can also fix purses, drawers and clips in various ways, and you can also step on them with your feet. I started to tie a rubber band. Because the rubber band is thin, I need to wrap it around several times and finally tie a fast knot.