Shop › Circular Chain Knocker, with 1/2" UNC Threaded end Image 1 of 1 Circular Chain Knocker, with 1/2" UNC Threaded end from $108.00 Pipe Size: Select Pipe Size 75mm (3") 100mm (4") 125mm (5") 150mm (6") 200mm (8") 250mm (10") Quantity: Add To Cart Added!