Torque Values and Tapered Threads – Do They Go Together?


Over the past few weeks, I have been working on various cars in the garage with some good friends. We generally get together and help each other out to make the jobs go easier as well as help each other learn more about keeping our family’s vehicles safe and even helping out some others that don’t have the means to work on their own vehicles. Throughout these repairs, we always end up in some type of discussion over something fairly technical. Sometimes it is the proper installation of a part such as take the bolts to snug, back them out, then torque to half the total torque value, back off again, then finally tighten to the complete torque.

We also share different ways of doing the jobs, such as how to lessen the amount of hot oil you are about to pour all over your hand, or how to get that rusted bolt out without a torch and without breaking it. One discussion that comes up quite frequently is torque specs and then the torque spec for a tapered thread.

In case you were not aware, the NPT or BSPT (male) inlets on EXAIR products are both a tapered thread. Tapered threads are generally used on pipe fittings under pressure to seal better and provide a secure engagement. When comparing this to a standard bolt, or straight thread, one is generally accustomed to receiving a torque spec on just how tight to get the fitting or threaded product. For example, the 1/4-20 bolts used in our Super Air Knives are torqued to 7.5 ft-lbs. in order to properly seal the cap, shim, and body together. These are straight threads and thus a torque spec is often driven by the material, size, and thread of the bolt. Torque on tapered threads such as NPT or BSPT fittings is not as easy to find, and not really reliable.

For tapered threads, the engagement of the thread is not always at the same point due to differing tolerances on thread dimensions. These differences create different points of thread engagement with the corresponding thread it is tightening into. For these scenarios, the torque specification is not always best suited as a numeric value. If you search hard enough you can find a table like the one shown below, but again, not the best value to use when installing a tapered thread.

Size in-lbs N-m
1/16″ 5 0.57
1/8″ 7 0.79
1/4″ 16 1.81
3/8″ 23 2.6
1/2″ 30 3.39
3/4″ 54 6.1
1″ 78 8.81

I personally would not use a straight numeric torque when tightening something with stainless steel thread into a brass fitting, or other dissimilar materials together. For this scenario, I would recommend using something like the table below. The TPFT value is, turns past finger tight. This means you would snug the super air nozzle, vortex tube, or other fittings by hand to finger tight. Then using a wrench or two if needed, turn the fitting to the correct number of revolutions for the given thread size. By utilizing this method and the correct amount of thread sealant, see John Ball’s video blog below, you can ensure there will not be a concern on whether or not the joint will leak and also if the fitting is tight enough.

1/8″ 2-3
1/4″ 2-3
3/8″ 2-3
1/2″ 2-3
3/4″ 2-3
1″ 1.5-2.5

If you would like to discuss torque settings, installation of your engineered compressed air solution, or even what might be wrong with your minivan, contact us.

Brian Farno
Application Engineer/Garage Mechanic Extraordinaire

Video Blog: How To Clean & Replace Emitter Points for the Ion Air Gun & Ion Air Jet

This video will give a thorough walk-through on how to clean the emitter point on EXAIR Ion Air Jets model 8194 and Ion Air Guns model 8193.  This is the same procedure for replacing a damaged emitter point.  This procedure is for new style Static Eliminators with integrated grounded terminals, released on February 1, 2016.

Brian Farno
Application Engineer Manager

Just The Tip Of The Iceberg

Over the past few weeks I have started to really look at the seemingly endless “Honey-Do” list for around my house.   As Russ Bowman mentioned a few blogs back it is still fairly cold here in Ohio so I immediately removed anything that has to do with being outside or the garage.   I decided to finally tackle the smallest room, the bathroom.

You see, our house was built in 1951 by skilled workers and has only had one other family live in it than mine.   The original family had a woodworker in it because I find lots of detailed cuts and trims that you don’t see in other homes so I know the house was well cared for.  In the 8 or 9 years we have been there we  have had the normal joys of home ownership but nothing that I couldn’t handle.   That is of course until we decided to spruce up the bathroom.

The bathroom was the one room we hadn’t done anything to and you could tell.   I decided it was at least time to repair the cracks in the walls and slap on some fresh paint, maybe a new medicine cabinet, and some other updates.   Well, what was once merely a crack in paint quickly evolved to the entire bathroom now needs a skim coat of joint compound.

What was once just a crack in paint is not an entire wall scraped to the plaster.
What was once just a crack in paint is now an entire wall scraped to the plaster.

This all happened in the course of about 5 minutes.   I just started to scrape the crack to get the loose paint off and sure enough it turned into what is shown above.   The bad news is the crack runs the full length of the wall and this is only a third of the wall.  Needless to say, I am now in over my head but am willing to give the repair a shot on my own but have already called in backup just in case.

Compressed air systems may have a lot of characteristics in common with my honey-do list.  The small issues may go for years without being checked or fixed, the list of items needing looked at may be growing daily.  Even worse, what you think might be just a small leak that doesn’t amount to much could actually be just the tip of the iceberg.   Instead of putting off the maintenance and the list of items to look at on your compressed air system, start checking those items off today.   If you don’t have a list, take a look at our 6 steps to compressed air optimization.   A little work now can save a lot of money later on.

EXAIR Six Steps To Optimizing Your Compressed Air System
EXAIR’s Six Steps To Optimizing Your Compressed Air System


Brian Farno
Application Engineer