Eco-Blu IDGMT151 1.5" MPT Return Fitting - Dark Grey Patent pending self-regulating variable orifice design Improved agitation quality which will help debris be pushed more effectively towards the skimmers creating a healthier pool environment The iBall achieves proper flow velocity which creates proper surface agitation and circulation at lower pump speeds. Automatically opens up to full orifice size when pump is at full speed Creates an overall efficient pool system, allowing the pool owner to spend less time on maintenance