Without a proper match between tubes and fittings, connections can be pulled off by vibration or tension, blown off from a pressure spike, or leak just enough to cause problems. Finding the proper connection is essential for a safe and secure system for everything from oxygen to viscous substances such as blood and medicines.

A metal connector is often the best choice for high-pressure applications, for handling certain chemicals and compounds, or where the environment can be rough. Yet just because metal is an inherently stronger material doesn't mean metal connectors provide a gripping force superior to plastic connectors. With high-quality plastic connectors, the gripping edge of the barb can be molded precisely with such a small radius, it's sharp enough to grab, but not so sharp it cuts the tube. This is not always the case with barbs on metal connectors. Different manufacturing steps, such as applying a plating layer to the metal connector, create a radius over the barb that dulls the gripping and sealing edge. In terms of gripping tubing and holding the pressure, plastic barbs can perform equally well, if not better, than metal barbs. In addition, plastic connectors generally cost less.

Of course, not all plastic connectors are created equal. In making a plastic part, a mold closes and opens to produce each piece. This process creates a parting line, a seam that produces a slight imperfection on the plastic part where the two halves of the mold meet. On a connector barb, a mold parting line can invite leaks. Parting lines are especially prevalent and obvious with poorly molded parts or where the manufacturer has skimped on maintenance and investment in mold tooling.

Mold parting lines on barbs can present a significant frailty for plastic connectors with hose barbs. To remedy the situation, look for manufacturers that create parting-line-free hose barbs or control the parting line to a nearly invisible witness line. Advanced molding allows extending the mold-parting line from the body of the connector to no further than the base of barb. Doing this is more expensive but it ensures a smooth, uniform surface on the barb that is necessary for a tight grip and seal.

Many applications require a consistent flow path for steady delivery of materials and to avoid damaging the media, such as blood, as it is delivered through tubing. The pathway along tubing is always smooth. The connections, however, pose issues where material can eddy or meet obstacles that actually damage sensitive material.

To achieve a consistent flow path, manufacturers create a sharper, tapered leading edge inside the barb. The edge faces oncoming fluids or gases moving through the tubing system. This design detail helps fluids move unencumbered through the connection, removing any entrapment areas where material can coagulate, easing fluids through the connection area with a tapered inside wall. In addition, a sharper leading edge helps reduce damage to sensitive media that can occur with connectors machined or molded with more blunt leading edges.

Even though fittings and couplings are not the same, these tubing terminations are often lumped together for evaluation. For example, when someone removes a tube from a simple fitting only to have blood splatter around the room, the problem is misdiagnosed as a problem fitting, even though a quick-disconnect coupling would have prevented the incident.

On a purchase order, fittings appear to be cheaper than couplings — and with good reason. The quick-disconnect coupling, intended to limit fluid release, is an intricate device with internal shutoff valves, latches, and other features that allow a secure connection on a repeatable basis without recutting tubing between uses. In general, quick disconnect couplings are specified for handling tubing that is connected and disconnected repeatedly. Hose-barb fittings are a means to connect tubing — not disconnect it. Couplings safely disconnect tubing. Couplings are more flexible than simple fittings, and safer, with features such as non-spill shutoff valves. By automatically stopping the flow, there is little risk of messy fluid spills or pressure loss on critical equipment when disconnecting tubing.