I talked about this whistle here in a previous post. During a recent trip home I took some pictures to share. I did not unroll the whistle to get measurements. Near as I could tell, it is made from a piece of tin in a T shape, with the top arms of the T being not quite 3x longer than and 2x as wide as the base of the T. The base is rolled to make the sounding area, and the arms are folded around to make the part you blow through. To make the whistle work, you must hold your thumb and finger over either side of the sounding area to make an enclosure. Think of how a coach's whistle has round sides. With this whistle, your fingers have to be the sides. Then you adjust the gap so that when you blow through the mouth piece the air whistles over the edge.