Nuts are only half of… Ferrule that’s doing most of the work! While the nut provides the driving force for compression, it’s the ferrule that compresses against the tubing and thus holds the tubing in place.

Ferrules aren’t nearly as complicated as their nut counterparts, but they do have some distinguishing features to help you determine which ones to use. One thing they have in common is their tapered noses…and it’s at the end of this nose where ferrules do what they were designed to do — grip the tubing wall!

When selecting the correct fitting for a given application, the following should be considered:

• tubing size
• pressure requirements
• mating nut
• receiving port geometry – most important

Picture 1: Different between ferrule configurations.

Generally, low pressure receiving ports end in a flat-bottom configuration. The ferrules used with this type of port will typically have their tapered noses facing toward the nut and away from the flat bottom of the receiving port.

High pressure receiving ports have an internal taper just past the threaded portion of the port. Then, just beyond the internal taper is a small pocket — often called the “tubing pocket” — which is nearly the same diameter as the tubing that extends into it. In these types of ports, the tapered nose of the ferrule faces away from the nut and toward the port.

“Tapered noses face the port when pressures are high but they face the nut when low pressures apply!”

One very important characteristic of any ferrule is the material from which it is made. Ferrules are often manufactured from materials such as stainless steel, PEEK, ETFE, polypropylene and PCTFE. Materials such as PEEK polymer (a beige-colored plastic), PCTFE, and stainless steel are often used to manufacture ferrules for high pressure applications. Softer polymers, including ETFE and polypropylene, are used primarily (although not solely) in lower-pressure applications.

Check out our range of HPLC consumables from IDEX, VICI and Optimize Technologies. Are you still hesitating which nut and ferrule combination to choose for your connection? Contact us and we will be happy to advise you.