What you should know about the BOLA HPLC Screw Joint System

This system is based on flanged tubing and UNF ¼” 28 G threads. These threads have their origin in the United States and are mainly used in chromatography/HPLC.” ¼”” stands for the outer diameter of 6,35 mm. “28 G” stands for 28 thread pitches at the length of one inch (25,4 mm).

Following tubing sizes are mainly used in HPLC:
» 1/8” (O.D. approx. 3,2 mm x I.D. approx. 1,6 mm)
» 1/16” (O.D. approx. 1,6 mm x I.D. approx. 0,8 mm)

The screw joint itself consists of a screw (BOLA Tube End Fitting) with washer and flanged tubing. It resists pressures up to 30 bar.

The metal-free washer provides ideal contact pressure of the flanged tubing and prevents small folds during the last phase of tightening the tube end fitting.

The flowing product is only exposed to PTFE – the screw joint has a universal chemical resistance and is absolutely clean.

The PTFE tubing to be flanged must be made of a special type of PTFE. Our tubing fulfils this requirement (see page 198). Besides PTFE tubing, there can also be used FEP and PFA tubing (both gastight and transparent).

The different colours of the tube end fittings can be used for distinction.

How to flange PTFE tubing

• cut tubing square
• clamp tubing by means of tubing holder – overhang approx. 3-5 mm
• press tubing on flanging tip and preform it
• press preformed tubing end on cooling plate
• push fitting and washer on the tubing and tighten the fitting
• ready.

Of course we also have flanged tubing with assembled tube endfittings in different lengths in our standard range.

Don’t confuse UNF ¼” 28 G and M6 threads!

Besides the common UNF threads, there are also M6 threads circulating. These threads are very similar to the UNF thread, but please only use UNF tube end fittings to avoid damage or leakage of your fittings.