EXP Fittings: Which Nut Do I Need?

Our brilliant friends at Optimize Technologies are continually innovating and making our lab lives easier. We love their patented EXP Titanium Hybrid Ferrule technology that is truly universal. You can use it on any tubing, any 10-32-port, any instrument—wrench-tight to 20,000 psi. This fully UHPLC-capable EXP ferrule is used with all EXP nuts. Restek offers three EXP nuts: hand-tight, hex-head, and EXP2.

The question is, which nut do I need? I’ve tried them all and found that it is truly situational. Ask yourself: how much space do I have, how often will I make-and-break the connection, and am I connecting PEEK or stainless steel (SS) tubing? Here are two examples.

The EXP hand-tight nut is ideal for column connections, especially on systems operating </=600 bar. Most column ovens in HPLC or intermediate-HPLC instruments are large enough to allow the hand-tight nut. Its larger and more-ergonomic head allows easy hand-tightening for repeated connections up to 8,700 psi. No wrenches, just fingers. While you certainly can wrench-tighten the hand-tight nut to provide leak-tight seals up to 20,000psi, the EXP2 nut is perfect for UHPLC applications. The torque driver allows a wrench-tight seal that’s as easy as finger-tight.

Alternatively, in the super-tight space of a 6-port injection valve, the EXP hand-tight nut won’t fit. The EXP2 nut is ideal in this situation. Its slim profile and torque driver allow flawless, fast, zero-dead-volume connections in places that traditional wrenches don’t fit.

If you’re using PEEK tubing, move to a hex-head nut. EXP2 fittings aren’t recommended for use with PEEK tubing. This is because the torque driver that’s included with the fittings is so effective, that’s it’s easy to crush your tubing. So if you’re using PEEK tubing and have minimal access or space, use the EXP hex-head fittings. If you just can’t fit a traditional wrench in there, try using the socket side of the ValvTool Wrench (find it here http://www.restek.com/p/25321). It’s slotted to fit over the tubing and slimmer than traditional wrenches.

Also, consider staggering the height of the nuts around your 6-port injection valve. EXP Hex-Head fittings come in three lengths: short, standard, and long. Varying the height allows breathing room for your wrench. An example of that is shown below.

Most analysts who try EXP fittings keep using EXP fittings, because they’re truly universal, extremely well-designed and durable, and easy. Please let us know what you think of them!