The 40's insert is a narrower version of the 70's, designed for the Snareweight JR. They respond to harder hits with some intentional movement, making it ideal for drummers that want variation while playing. They also tend to give the snare the MOST possible high end presence when dampening. ** can even be used on the new snareweight #5. Comes as a pair.** dims- each side is 4.5 inches long x 1.30 inches wide tip "use just one instead of two for a brighter sound, or turn upside down for more highs"