The square 3/4?x3/4? opening through the block allows you to work in the middle area of the block without fear of bending ear posts, bails or other delicate details on the back (or FRONT!) of your jewelry pieces. Burnish or brush with as much pressure as you want without breaking or bending projections on the opposite side. Now you have four solid sides and two ?open? sides making the block lighter, easier to handle and so much more versatile.