This Harmony ZB, clear silicone boot is compatible with Harmony XB4 and XB5 double heads with two flush buttons.This silicone boot covers your Harmony XB4 or XB5 double heads to prevent dirt and other contaminants from proliferating.It is chemical resistant, making it ideal for operation in harsh environments requiring frequent chemical cleaning.The silicon boot prevents growth of bacteria in joints and gaps, this makes it ideal for high hygiene environments like food and beverage industry.