There are grooves at the bottom of Shimano spinning reel spools that will cut Spectra braided fishing line. (See attached photos.) Background A while ago, I tried connecting some hollow core Spectra line to a Stella spool and had bad results. (Connecting to Spool) At the time, I believed the fracture of the Spectra was due to stretching around a tight radius spool with thick mono inside. This morning, I was taking a photo series of Spectra attachment to a different Shimano spool. When I began to load the 80# line (actual break above 105 lbs.) with 75 pounds of tension, the line fractured (ripped) as shown in the photo series below. The line broke right where it contacted the groove in the spool. I often test line and knots and pull on Spectra with a tool of the same radius as the spool; it never rips, breaks or fractures. I have also performed this test with a Penn spool, no grooves, no problem. Cause There are very sharp (90 degrees) grooves machined into the bottom of Stella, Saragosa and Stradic (not sure about others models) spinning reel spools. My believe is they are there to give added traction to mono connections but I haven't contacted Shimano. (I've added a couple extra photos of Stella and Saragosa in addition to the Stradic sequence.) Fix The Spectra line has to be isolated from the machined grooves. A layer or two of tape may do the job but I can't say for sure whether the grooves can cut through the tape. A couple layers of thin mono may also do the job. Perhaps the grooves can be filled with epoxy. Side Note My original purpose was to demonstate that Spectra won't slip on the spool. That test was a complete success. No tape or other measures are needed. But those sharp grooves are killers!