How can I use Raptor columns and the EXP Direct connect holder with stainless steel fittings?

Some customers may find themselves with this scenario. You have an HPLC instrument with existing stainless steel tubing and fittings and you are getting ready to install a Raptor column. The end of your tubing may very well look like the one shown above. Here are some questions you might have.


Can I attach this stainless steel fitting directly to a Raptor or other Restek LC column?

Yes, this is possible to do with a Raptor column or any of our Restek LC columns. To form the best seal and avoid leakage, it is preferred to start with a nut and ferrule that is not already swaged (tightened down). To obtain the best seal, insert the tubing until it bottoms out and then tighten the fitting. The difference between using stainless steel fittings and PEEK type fittings is discussed further here in the FAQs section of our website:


Can I attach this stainless steel fitting directly to an EXP Direct Connect Guard holder (catalog #25808)?

Again, yes this is possible, and the same conditions apply that I mentioned for connecting directly to the column. Particularly if you intend to operate up to 600 Bar, it would be best to start with a nut and ferrule that is not already swaged to obtain the best seal.


Is it better to use some other type of fitting to connect to a Raptor column or EXP Direct Connect holder?

We prefer to use an EXP fitting to connect a Raptor column or the EXP guard holder for several reasons.

Reason # 1:  Usually you can tighten the EXP fittings by hand and will not need a wrench. Not only is this just a whole lot easier, but it results in a longer lifetime for the end fitting of the Raptor column, or longer lifetime for the end fitting on the EXP holder (called a “holder cap”) in the figure below.


Reason #2: The EXP fittings will work with either PEEK tubing or stainless steel tubing.  If using stainless steel tubing, EXP2 fittings (shown below), may also be used, but these are tightened with a driver nut that comes with the fitting when you purchase it.

Reason #3:  As mentioned in the above link to the FAQs, the EXP fittings do not require permanent swaging. This means that unless you use a wrench to tighten it, the ferrules are removable and can be reused.   Please note that ferrules used with EXP2 fittings are also somewhat reusable, even though a more permanent seal is created that is rated up to 20, 000 psi.


How would I go about using an EXP fitting to attach my column or guard holder if I already have the stainless steel nut and ferrule swaged to the end of my tubing?

This is the tricky question and there are several different ways at least to do this.











Option #1: Replace this section of tubing with PEEK tubing and add EXP fittings to both ends. Particularly if you don’t plan to operate above 600 bar on this instrument, the PEEK tubing will be easier to work with and it is preferred by most analysts.  You will find our selection of PEEK tubing here on our website:

EXP fittings can be found here:



Option #2: Since we do not recommend cutting the stainless steel tubing, the swaged nut and ferrule cannot be easily removed. If for some reason, you need to continue using stainless steel tubing, you can just replace the length of stainless steel tubing with a new one. We sell lengths of ss tubing here on our website:  You will need to check your instrument manual to see which tubing ID it recommends for this instrument model. In many cases, this length of tubing is 0.17 mm or 0.007 inches ID. If you plan to use a tubing assembly that already has stainless steel fittings on it, make sure you start with one that is not swaged yet on the end that goes to the column (so you can remove the nut and ferrule).  You can then use either EXP or EXP2 fittings to attach the column. Most likely, you can use the same type of fitting at the other end also.









Option #3: This is the most creative and versatile option. If you want to keep the existing stainless steel tubing and fittings in place, but prefer to use an EXP (or EXP2) fitting to attach your column or guard holder, this is what you need to do:

Attach a zero dead volume union, such as our catalog #20147, or something similar with 10-32 threads (most typically used for LC) to the existing stainless steel fitting. The bore size of the union should be as close to the ID of your tubing as possible. If the union comes with metal nuts and ferrules, you will not need them.

Obtain an EXP coupler, catalog #25940. Attach one end to the union and the other end to the Raptor column or the EXP Direct Connect guard holder (catalog # 25808). Once tightened down, you should be ready to go.


I hope you have found this post helpful. Thank you for reading.




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