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How to Identify Which Stainless Steel Tube Fitting you Need and Tips for Selecting The Right Tubing

In this article we will discuss our top pick for the highest quality stainless steel tube fittings, how to identify which fitting you need for your tubing and how to select the proper tubing to ensure the highest level of mechanical integrity is maintained during installation of the fitting and throughout the duration of its use as part of any system!


Our Pick: S-LOK Stainless Steel Tube Fittings

Industrial Service Components has been working with machinery and various systems where a highly reliable industry specific fitting is necessary since 1991. We have seen our fair share of high quality tube fittings, and dealt with the aftermath of many low quality fittings as well. Throughout the years we have come to recognize S-LOK tube fittings as one of the top rated, most reliable and well built tube fittings on the market! S-LOK fittings are specifically designed for high demand manufacturing applications where various chemicals are used such as petroleum, power generation, pulp, paper and other more! One of the most common applications of S-LOK tube fittings is instrumentation, process & Control systems where there can be no compromise on the quality of tube fitting used.

There are many reasons why we consider S-LOK to be arguably the highest quality tube fitting on the market. First, S-LOK fittings are manufactured under extremely strict quality control measures to ensure they are the most reliable they can possibly be in their performance. These fittings are convenient but not to be underestimated! They do not require specific tools for assembly or installation and can be installed quickly with great confidence that the likelihood of leakage is close to none

S-LOK Tube fittings are made up of four parts that ensure the fitting is built for precision. The body, nut, front ferrule and back ferrule. These four pieces operate extremely efficiently. When the nut is fastened onto the body, it is tightened against the tapered area of the fittings body, causing compression on the edge of the fitting forcing the edge to curl inward against the tubing. The twin ferrule design, operates as a biting effect when both the front ferrule and back ferrule roll onto the tubing, ensuring leak free seal is made without risking the tubing becoming stressed or depressed!

S-LOK Fittings are made of three separate materials depending on the application: Stainless Steel, Brass and Alloy Steel . The temperature of the fitting application will have a huge role in which material is required for your tubing, but this article focused on Stainless Steel Fittings.

Selecting the Proper Fitting:

S-Lok Tube Fittings come with individual part numbers for each specified size, shape and type of fitting, that make identifying which fitting you need easy if you know what to look for! The following is an example of an S-LOK Tube fitting Manufacture Part Number for a Tube to Pipe End Fitting:


What does all this mean? Well its quite simple actually! The first letter in the part number S, is the identifier that the fitting is a double ferrule tube fitting made by S-LOK. The second and Third letters, in this example: MC is the fitting type identifier. In this case, the connection of the fitting is a Male NPT connection. MC stands for "Male Connector". The second section of the fitting MPN is 4M, this is crucial because this identified the tubes outside diameter. In this case M stands for millimeters and 4 is the number of millimeters. It is extremely important to get this number correct when choosing which fitting you need because if if the fitting o.d designation is larger than the tubing o.d. which you are using, the fitting will leak, and if it is smaller, the fitting will not fit onto the tubing. The next section of the fitting MPN in 4R. 4 is used to identify the pipe thread designations, in this case 4 is 1/4" and R is used to identify the thread symbol of pipe thread. The last section of the Fitting MPN is S6 and this is simply a material designator for the fitting which you are using.

The figures below provide charts for Tube O.D. Designation, Pipe thread size Designation Pipe Thread Symbol Specifications and Fitting Material Designation that you will see on various MPN for S-LOK fittings.

Now that we've identified how to figure out which Tube to Pipe end Fitting You need, what about Tube to Tube End fittings? Take a look at the following S-LOK part number for a tube to tube end fitting:


Since we have already deconstructed one type of S-LOK fitting, this one will be a bit simpler. We know that the first letter in the MPN Sequence is the S-LOK tube fitting identifier letter S that means "Double Ferrule". The Next Letter, in the sequence is the T , and this is the fitting type identifier, in this case the fitting would be a union T fitting. The second section, similarly to the previous part number we discussed is 8M. We already know that this is the designation for the Tubes O.D. and it means that the fitting is appropriate for a tubing connection that is 8mm in diameter. Finally, the last section of the Part number is S6 and as discussed previously, this is the designation for what material the tube fitting is made of: in this case stainless steel.

Below is a chart of the various SLOK fitting types that we supply, depending on the shape and direction of connection you are trying to make.

Please note that there are hundreds of S-LOK connector sizes and variations that fall under these fitting types, we strongly suggest calling or visiting Industrial Service Components Inc, as we are an authorized distributor for these fittings local to the Vancouver Washington area and can make sure you get the right fitting without any mixup! Walk ins to our Vancouver, Wa. (Not B.C. Sorry) location are encouraged!



Selecting the appropriate tubing to ensure reliability and a high performance level!

A suitable tubing selection is essential to ensure the performance of tubing systems as well as S-LOK tube fittings.

Here are 6 general rules to follow when selecting tubing for a system to ensure the tubing is rated for the pressure, flow, temperature and environment of the system!

  1. Make sure that tubing being used has a surface that is free from scratches, draw marks, flat spots or dirt and other debris. This will ensure the leak-free sealing is effective.

  2. If welded tubing is being used, it is imperative that there is never a visible poor bead on the tubes outside diameter.

  3. Make sure that the tubing you are using is compatible with processing the fluid type, temperature and the environment that is will be installed in.

  4. Tubing must be softer than fitting material.

  5. Tubing Hardness needs to be selected according to the information in the following below.

  6. Ensure that the wall of the tubing you select is not too thin or too thick. if the wall is too thin, the tubing may collapse and if it is too thick, the tubing will become deformed by the ferrule function of the fittings.

Please see the tables below in reference to tip number 5.

The information in this article is readily available in a much more in depth PDF linked to the bottom of this blog post.

If you are still confused, or would like to contact us with questions about the proper tubing or tube fitting application we strongly encourage you to call us at (360) 597-3061 for professional help with selecting a high quality tube fitting and tubing pair for your system!


(360) 597-3061


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