This is a replacement magnetic flap for the water flow sensors used in the Bestway, Coleman and Lay-Z-Spa brands of inflatable hot tubs. If your pump/heater unit is displaying an E02 error and you find that your magnet is rusty due to the plastic cracking or other things like the one to the left, you should replace it with a new one as it is the most likely cause of your E02 error. The fully assembled flow sensors are selling for between $50 and $75. Why spend all that money when you can repair this yourself. The part you are buying is a 3D printed version made from ABS plastic with the magnet completely sealed to prevent it from being exposed to the water and rusting yet again. Other 3D printed versions like the one to the right seen on Ebay and other sites have the magnet exposed which will cause quick failure of the part due to the exposure of the magnet to water. Be weary of these and do not buy them.