Technical Information

Determination of thread types

In daily practice it is often necessary to choose a suitable fitting. Due to the multitude of different threads this is not always easy. The following drawings shall give you some assistance.

Like shown on the picture, it can be helpful to determine the thread size by putting it on our drawing which is, of course, in full size. Also all information on outer diameter and thread pitchGlossarythread pitchDistance from thread tip to thread tip (i. e. distance from thread tip to thread tip) can be determined with a little skill. The form can mostly be recognised easily.

We will help you should you still have problems in determining your thread. Just send us a sample or counterpiece, we will be glad to help you with your choice. But please understand that we are not able to determine fitting threads on faxed copies.

NPT (National Pipe Taper) thread

American pipe thread or BSP (British Standard Pipe) thread
Easy recognisable by its tapered outer and inner diameter which is selfsealing.
Therefore, NPT threads are also known as “sealing thread” or “tightly threaded connection”.

R or G thread (Whitworth)

Cylindrical threads which are mainly used in countries with imperialGlossaryimperial A system of units based on Inches. In Europe, the imperial system (which is still very common in the USA) has been replaced by the metric system. With BOLA Tube Fittings and Reducing Unions, a transition from metric to imperial tubing can easily be made. The conversion from mm to inch can be found here. system. The size of e. g. R 3/4" does not stand for a diameter. Thus the corresponding size has to be determined according to charts.

M thread (metricGlossarymetric The metric system is an international decimalised system of measurement. In Europe, the system was introduced in the 19th century to achieve international comparability. With BOLA Tube Fittings and Reducing Unions, a transition from metric to imperialGlossaryimperial A system of units based on Inches. In Europe, the imperial system (which is still very common in the USA) has been replaced by the metric system. With BOLA Tube Fittings and Reducing Unions, a transition from metric to imperial tubing can easily be made. The conversion from mm to inch can be found here. tubing can easily be made. The conversion from mm to inch can be found here. ISO-thread) – standard in Europe

Cylindrical inner and outer diameter which is precise in millimetres. The extremely fine taper of this thread allows the best possible force transmission. MetricGlossaryMetric The metric system is an international decimalised system of measurement. In Europe, the system was introduced in the 19th century to achieve international comparability. With BOLA Tube Fittings and Reducing Unions, a transition from metric to imperial tubing can easily be made. The conversion from mm to inch can be found here. threads are designated by a capital M plus an indication of their nominal outer diameter, for instance M 10. A taper deviating from the standard is marked with an appendix like for instance M 10 x 0.75.

UNF 1/4"-28G thread

It has its origin in the USA. Mainly used in chromatography/HPLC applications. Most common sizes are UNF 1/4"-28G and UNF 10-32G. The digits 28 G and 32 G stand for the number of thread pitches at a length of one inch (25.4 mm).

UNF 1/4"-28G versus M 6

Without exception all BOLA HPLC fittings come with the most common HPLC thread UNF 1/4"-28G. In addition, fittings and distributors with the very similar thread M 6 are used. These threads can only be distinguished by exact determination of their outer diameter or by using a test mandrel (it is possible to screw in a tube end fitting in the counterpart of the other thread for at least 2-3 rotations). The UNF 1/4" thread has an outer diameter of 6.35 mm, the M 6 thread has precisely 6 mm (work tolerances are possible). We recommend to use only the UNF 1/4"-28G thread to avoid confusion and double inventory.

BARREL THREADS

GL-threads

GL threads are round threads, i. e. there are only round and no sharp ends at the flanks of the screw thread. Due to its simple shape and the round ends of the flanks, this thread can easily be formed on glass pipes. The extremely high pitch and the large flanks give this thread an important carrying power.