The original Betty Bridge was designed to solve the problem of the difference in height on your sewing machines bed or surround, causing seam allowances to get caught and flip during sewing. The Betty Bridge Supreme offers the same great features with the addition of ruler guides. To use the Betty Bridge Supreme, peel the back paper off and place the Betty Bridge Supreme on the bed or surround of your machine (sewing or serger). The surface that had the difference in height is now smooth! Seam allowances will glide through and not get caught and flip during sewing. * DO NOT PLACE OVER FEED-DOGS Some machines have a drop-in bobbin, or there may be a divot in front of the needle that could be a problem. The Betty Bridge Supreme will help with this also. Another use: When joining pieces together, make sure edges are lined up evenly. If the bottom piece is a light value and your sewing table is light, it will be difficult to establish alignment. Place the Betty Bridge Supreme under your pieces so alignment is easier to see. Each package contains two repositionable Betty Bridge Supremes. Simply peel backing off and stick down.