This plastic seam guide by Lori Holt of Bee in my Bonnet is an acrylic template for measuring accurate 1/4" seams and for constructing easy corner triangles.
Position your sewing machine needle into the centering dot, cut the template, and put the stickies under your template. It will save you time by not having to mark your fabric when sewing half square triangles, flying geese, or snowballs. The center circle of the guide is marked with 1/2" grid lines for projects with a wider seam allowance. Four stickies are included to temporarily adhere to any sewing machine or serger.