The Multi-step reducer consists of 4 fittings that fit neatly one inside the other. You can use all four, just three, a pair or you can use them individually. Each section has a slight taper to accommodate variations in the internal hose diameter. For instance, the largest section has an outer diameter of 98mm and is a snug fit inside 100mm extractor hose. This fitting also provides an inexpensive and practical solution to connecting different size vacuum hoses in order to gain extra length.