On my sewing machine I have a buttonhole sewing setting but it's not big enough for what I need (i.e. a strap hole rather than a button hole) which stich can I use to ensure the raw edge of the hole doesn't fray?
Are you using an automatic buttonholer? If yes, then sew up the side seam remove the largest button it will take (usually step 2), move the buttonhole foot back to the beginning, pop in the button again, repeat until you have the size you desire. Repeat again on step 4