If you have ever ended up with two pieces of hose that are just a bit too short for your project, you'll love this joiner!  The black anodized aluminum tube has barbs at each end for positive hose retention, plus a centering ridge in the middle to ensure that each hose is fully seated.  
The 1/2" OD is designed to splice together any two 1/2" ID rubber hoses (fuel, water, oil, etc).  Keep a couple in your toolbox for emergencies like a kinked or punctured hose, re-routing a hose away from abrasion or heat, or bypassing a clogged filter.  Sold individually.  Hose clamps are not included.