Stack & Whack and OBW's are both types of kaleidoscope blocks. S&W blocks can vary in looks and form and are set with sashing in between the blocks. More than one fabric is used in the blocks. S&W is the term coined by Bethany Reynolds in her book. OBW blocks are all made identically from one fabric. It is the way the fabric is cut that makes the kaleidoscope variations. OBW blocks are sewn together without sashing. OBW is the term coined bt Maxine Rosenthal in her book.