The collar nut fits all Mr. Soaker Hose Timers. This is the piece between the female threaded end and the timer itself. It basically acts as a "union" between the two. The collar is NOT a warranty item. If your pet bumps the timer or if you pull the hose and brake the collar nut, you'll need to buy a new one. This is a replacement part. You do not have to purchase this item when purchasing a timer.