That little knob is to change the stitch length.
To the right makes it larger, to the left smaller.
As for the belt, send a PM to Mizkaki...she'll get you hooked up. I don't buy "belts"...even tho I probably should, instead I use leather boot laces, usually 72 inch and cut them to size, connect them with either the old staple from the "original" belt, I've been known to use a bent, cut to length paper clip, or you can sew the ends together with dental floss.