This two-way inflation Bestway Screw Valve, also known as a 'Boston Valve', is mainly used with Bestway Lay-z-spas, dingys and air mattresses but is also used on some Bestway Pools. It screws in to fit a 2cm diameter hole. Compatible with Lay-Z-Spa models except the Monaco, Napa, Helsinki and Singapore. Please Note: We recommend you measure the hole prior to ordering to make sure it is the correct size and part. Warning: Not suitable for children under 3 years. Warning: Only to be used in water in which the child is within its depth and under adult supervision.