KEMP USA 10-421 FOX40 Classic whistle is the standard choice for referees and coaches at all levels, rescue professionals, and general safety worldwide. Flawless, consistent, and reliable. The chambers are designed to self-clear when submerged in water. There are no moving parts to freeze, jam, or deteriorate. Whistle dimensions are 2" x 1" x 3/4". Assorted colors.