What is the difference between 3608 and 4710?

The Hydrostatic Design Stress (HDS) is different. When calculating for pressure ratings, the HDS of the resin is used to determine the Working Pressure Rating (WPR) of the fitting. For example, a fitting made from PE4710 and SDR 11 would be calculated as follows: 2 x HDS / SDR -1 2 x 1000 / 11 - 1 2000/10 200psi Conversely, a fitting made from PE3608 and the same SDR 11: 2 x HDS / SDR - 1 2 x 800 / 11 - 1 1600 / 10 160psi Two different pressure ratings and the Resistance to Slow Crack Growth and Stiffness is much improved vs. PE3608. You can use a PE4710 DR 11 fitting or pipe to replace a PE3608 DR 9 fitting or pipe and still have the same pressure rating of 200psi (so you can save on cost as well).