Well I guess I should post a link to the pattern on Fons and Porter as the half square triangle doesn't sew to another half square...I'm so sorry after your wonderful explanation luvspaper If you enlarge the picture an then see the black 6 3/8" point of the arrow then is sewn to the other pieces .... I hope that makes sense? https://www.shopfonsandporter.com/product/black-arrow-digital-pattern/shop-quilty/?template=sq