It's Sew Emma Sew Standard Seam Guide- 4-in-1 tool does quadruple duty as a ruler, seam guide, .25" marking tool for binding, and features a handy 45° line for trimming half-square triangles.

Includes 16 holes to set your stitch, between .13" and 2".

Made of fluorescent acrylic for visibility. Measures approximately 2.5"x 5.5".