Dixon 3700606C is a brass hose barb hex nipple with 3/4" male pipe thread on both ends. Designed for connecting hose to threaded fittings in industrial and agricultural applications. The hex center allows easy wrench installation.

This is a rigid white type of plastic that is mainly applied for vent and wastewater systems. In other cases, it can also be used for cold underground water supplies outside the houses as well as venting, drains, and irrigation piping. PVC is mainly white though it can also be available in gray. In water conservation, you can also get purple PVC pipes used for differentiating grey water from drinking water.

If you want to have a properly functioning plumbing system, the first step is to understand the fittings. This post is a comprehensive guide to help you understand plumbing, fittings, and their design.