D.T. SYSTEMS H2O Receiver Collar color:Green Receiver straight and 90°(optional) straight and 90°(optional) Self Locking Bow Shackle Diameter 8mm 5 16" Key Features:• Digital Technology• Adds to any H2O 1800 PLUS series training system(excluding Beeper models)• Replaces any lost or damaged H2O 1800 seriestraining system (excluding Beeper models)• Up to 1800 yard (1 mile) range• Lightweight and waterproof• MAXX Range Internal Antenna System• Rechargeable Ni MH batteries• Built in safety shut off system• Available Limited Lifetime WarrantyPackage Contents:• 1 x Collar Unit w Green collar belt• Double jack Cable The H2O Add On Collar unit can be added to any existing H2O 1800 PLUS series training system (excluding Beeper models) to expand your unit up to a 3 dog system