Westwood Spiralink 10034 Circulator Coupling Flexible Spring For Use With: Taco 121138 Series In Line Circulators 1/2 3/4 1 Circulator hp CW � No wear points lasts forever � Silent quiet and noise free � Tolerates misaligned shafts in 3 dimensions � Easy to install � 1/2 x 5/8 Inch and 5/8 Inchshaft