Pro Sportfisher Ultra Sonic Disc is the worlds&'; first vented brass disc. The Ultra Sonic Disc combines a little weight for the fly with vibrant, solid colours and improved mobility. Discs smaller than 7mm have very little effect, so we decided to start the diameters at 7mm increasing, in 2mm increments up to 11 mm for the biggest tubeflies. The Pro Ultra Sonic Disc shape is optimized to create a vortex around the fly, allowing soft modern materials to swim freely instead of collapsing in hard current. The venting holes allow for an easier lift off for a new cast. Pro Sportfisher Ultra Sonic Disc Specs Small (10 pcs/pk): 7 mm in size, 0.14 grams/2.16 grains in weight Medium (9 pcs/pk): 9 mm in size, 0.23 grams/3.55 grains in weight Large (8 pcs/pk): 11 mm in size, 0.36 grams/5.56 grains in weight Pro Sportfisher Ultra Sonic Disc fits Pro Microtube, Pro Nanotube, Pro Flexitube 40/40 and Pro Classic Medium tubing options