This pack of 25 #13 Standard Dri-Tube (long quill) is the most commonly used hearing aid tubing size, built with moisture-resistant PVC to reduce the build-up that can dull sound quality over time. Its standard wall thickness is sized to match the sound bore drilled into most earmolds, making it the correct default choice for routine tubing replacements and new fittings rather than earmolds specifically bored for a thicker-wall tube. Keep a pack on hand for everyday tubing swaps across the majority of BTE fittings.