I use a 1/4" piecing foot. It has a metal finger that rides along the edge of the fabric. Hence, always 1/4". A cheaper and easy way to achieve the 1/4" is to use a short stack of post-it notes. Just measure from the needle to 1/4" away and stick the post-its down. Doesn't leave any residue either. I use this method when teaching my young students to seam anything.