General description The 4 Pack R4 Climbing Pad is designed specifically for Maytronics Dolphin M200, M400, and M500 robotic pool cleaners. These underwater sponge pads enhance the cleaning efficiency of your pool robot by providing superior water absorption and climbing capabilities. Technical specifications Size: 3.62 inches Inner hole diameter: 1.89 inches Thickness: 1.02 inches Usage During use in water, the pads will harden as they dry, which is a normal characteristic of the material.