29 responses to “Trick of the Trade: Applying Teflon Tape”

  1. Chris Gammell

    Though my skills are hardly anything to brag about, I can usually spot a newbie’s soldering skill from a distance. Haha, I at least know how it SHOULD look! 🙂

  2. Commenter

    Your pictures and instructions look absolutely backwards for standard threaded parts. The trailing edge of your tape will be meeting the tightening female connector.

  3. Chris Zeh

    Wait, don’t your pictures show the incorrect wrapping direction? As you insert the fitting with this wrapping, rotating the adapter clockwise, the end of the tape will tend to loosen and come undone.

    I just spent the last few weekends plumbing my house and I spent a long time trying to decide which wrapping direction was correct. In the end I went with the opposite of what you picked. Maybe I’m mistaken?

    1. cryogenic plant

      Yes I am completely agree with Chris that the pictures shows it is in incorrect wrapping direction.

  4. Moiety

    Regarding the direction of the tape, just by looking at it I could not figure it out so I had to get my Swagelok pocket book out. Even then I had an issue so I am not sure. I tend to only use male joints. One that note if you are being pedantic, then what is shown is not the recommended direction unless you are connection to a situation where the thread direction is reversed (For example connecting to a flammable/toxic gas cylinder, clockwise=closed rule is reversed in Europe due to flam gap rules, don’t ask me why). When threading in, you want the screw to thread away from the leading edge.

    However that is really beside the point. If the Teflon leading edge is tight with the thread, it will usually not matter. If only matters when the Teflon is not tight or smooth. In cases where I need to use Teflon (very rare) I get a thread grove and flatten the Teflon in the direction of the thread.

    But again that is really beside the point. The most common mistake I see with teflon is that people use it when they should or must no use it. It is nearly always preferable to use a lubricant (like Swagelok goop) as you cannot use too much goop whereas you can use too much tape. Also the take will interact with the system if it is at temperature and pressure or if it experiences large changes. Also it can get stuck to the threads. Not only that but you may be taping a defective thread so close examination of the thread and nut should be done before taping (this is pretty common).

    The only times I tend to use Teflon is
    1. Persistent water leak where I have no alternative part or it is a push connection.
    2. Teflon or other plastic fittings
    3. Plastic to metal connection if my preferred way is not available (o ring seal)

    It is not wrong to use Teflon but more often than not, I see the incorrect application. That can have bad consequences at pressure.

  5. Jason

    I’m an automotive tech and electrical engineering major. As others have stated, you wrapped it backwards. It should be wrapped in the opposite direction that you’d be turning the male end.

    Moiety, a water leak need not be persistent to require the use of Teflon tape. There are some applications where it is standard practice as a way to avoid those situations. In many cases, the Teflon might not be a necessity to ensure a seal, but is still applied to help ensure that no leaks develop in the future. This is especially true in cases where a leak could have costly (or otherwise devastating) effects.

  6. billswift

    Besides the tape direction, there is the problem that often you can’t move or handle the pipe you are wrapping. The simple rule that you can use anytime is to start at the end and follow the direction of the threads.

    1. billswift

      An easier way to remember and visualize it, is to move the tape around the threads just like you would a fitting that you were screwing onto them.

  7. Moiety

    “This is especially true in cases where a leak could have costly (or otherwise devastating) effects.”

    I completely disagree. For such instrances where you have a potential devastating impact (such as loss of life or loss of production) you will definately not use Teflon tape in your seal. Dry thread with goop (if it is a thread connection) or a flange seal/o ring suitable for compression made from a suitable material (Teflon or other FKM like Kalrez, graphite etc) or configuration (compressed, spiral wound) is what is used in the petrochem industries.

    I understand that the tape is used in hopes to prevent future leaks and this is fine on water sytstems in general. However often the tape is not needed or suitable (if the connection is specified correctly) and you get a series of events which lead to the leak which would not have happened if the tape were not used (e.g. tape is incompatible to the temperature, pressure and process side fluids used). In that case people are using the tape to seal something that is often not fit for purpose in the first place.

    1. billswift

      That’s why I use goop when I am changing the gas piping in my house. I missed that part when I read it, I guess I was distracted too much by the pictures.

      1. billswift

        Not Goop, I meant pipe dope.

  8. Jason


    I should have been more clear. The systems where I typically see Teflon used are water systems (either automotive or household plumbing) and pneumatic systems where the tape is used on a tapered male thread. In those cases, the male thread could be tightened without the Teflon tape, in many cases without leaks. However, the lubrication provided by the tape allow for more easily assembly and sufficient clamping force (probably using the wrong term here as I’m not a ME), which ultimately ensures that no leaks occur. I’ve seen far too many cases where tape wasn’t used and leaks developed over time. Am I incorrect here? If so, I’d like to know.

  9. Moiety

    I agree with your applications as long as they are non critical (i.e. not on a water loine cooling a reactor). And yes tape will act as a lubricant.

    My thoughts are projected more towards the process industries where temperature and pressure especially will not allow teflon tape to be used. Indeed even with a large water tank, I have seen leaks in a tape system due to the pressure gegerated due to the hydraulic head.

    Per ASTM (American Society of Testing & Materials) Standards we must use a thread sealant on all NPT (National Pipe Taper) Threads & fittings.

    Why you are seeing threaded connections degrading over time is impossible to solve over this forum. However as well as sealing problems you could also consider wear and tare or incorrect installation (for 6 mm 1+1/4 rule applies).

  10. Scott Moorman

    A few things. Speaking in terms of straight industrial or mobile hydraulics…

    1. You CAN use too much “goop” or tape – you never want your sealant to get into the system you are trying to seal. (see #2)
    2. The tape should never go all the way to the bottom of the fitting as shown – any pieces that washed out will get into the system and can potentially contaminate any valves with tight clearances (spool valves, servo valves, etc.)
    3. Teflon tape is required on NPT fittings (technically not on NPTF) – it’s not just to fix leaks.
    4. “Goop” is too often used to correct underlying problems – if the tape doesn’t work, there is doing something else wrong.

    I was always taught to hold the fitting end that I am sealing pointed at my chest. Wrap in a clockwise direction startign about 2-3 threads from the end. Stretch it lightly as you wrap. Wrapping it in the wrong direction will often (unless you have very thin tape) cause it to bunch and spin up the threads – making it useless.

  11. Mehedi

    Good Post about how to use Teflon Tape.

  12. An old engineer

    How many of you are aware that for gas pipe fittings, there is a different type of “teflon” tape? Use the wrong type and the tape will start to deterioriate upon exposure to the natural gas.

    I had to tell a plumber who was installing a new water heater in my house that he needed to redo the gas fittings. He wasn’t happy about redoing the fittings, but he also knew I was right. He just didn’t want to go back to his truck to get the right type of tape.

    For larger pipe sizes, it’s better to use teflon paste instead of tape. The larger the pipe size, the bigger the voids between the threads.

    Lastly, if you ever work on the water valve fittings in your house, apply a thing coating of teflon paste on the brass ferule before you assemble the joint. It will help seal all of those microscopic voids and help seal the joint without having to overtighten the fitting.

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  14. Geoff

    You do occasionally run into people who actually prefer not to be shown the “tricks of the trade”. I have a young friend who is a biomedical scientist. For light relief she’s a race car driver and does her own maintenance. I sometimes help her out starting with the concepts behind something. Often the next time I see her the job has been done (and done well). I now start with “the things that might kill you” BEFORE I do concepts :-).

  15. Philip Ngai

    There are some subtle details in how NPT fittings leak. A path parallel to the long axis of the fitting is not the only way that a leak can occur.

    There is also a spiral leak path that can not be blocked just by tightening the fitting. Here is a picture:


  16. Mark Metcalf

    Leaks are caused by improperly assembled joints. Adding Teflon tape to most installations will only increase the chance of joint failure, not prevent it.

    1. Don’t over-tighten joints by giving them “one more turn to be sure.”
    Do finger tighten plus one or two turns- No More.
    2. Don’t wrap Teflon tape or Teflon paste or pipe dope to add bulk to or to lubricate the joint.
    3. Do use a sealant for threaded joints.
    4. Don’t use “stronger” Schedule 80 threaded fittings on the assumption that they may solve the problem of splitting through over-tightening.
    5. Do use only Schedule 40 threaded fittings with Schedule 40 pipe and fittings.

    A great article about the do’s and don’ts of threaded PVC joints can be found at: http://www.lascofittings.com/supportcenter/TheDosandDontsThreadedPlastic.asp They support their instructions with actual facts and engineering and it very informative to understand the process. It is also a quick one page read. Good luck!

  17. Curtis

    The easiest way i know how to put Teflon tape on the correct way is to hold the fitting in one hand, then put the tape on and apply the tape the same direction you would screw a nut on the fitting. It works for me.

  18. Jessey

    Here’s a tip: Now that the pictures are correct, remove all the comments about the pictures being wrong. Luckily I continued to read the comments until I got to the post stating that the pictures were changed. Others might not be so lucky and assume that the pictures are still incorrect.

  19. LeRoy

    Jessey is right on.

  20. Marcus

    For those saying the Teflon tape is wrapped in the wrong direction, remember that you want the start the tape at the top of the thread (where it enters the female end) and to have it overlap until you reach the free end (not overlapped) at the bottom of the thread. You DO NOT want the free end of the tape (not overlapped) at the beginning of the thread. Also NOTE that the direction arrow is NOT the direction she/he is turning the thread. It is the direction the pipe is being turned.

  21. Marcus

    To make it as simple as it gets:
    Start at the open end of the pipe. Wrap once around the edge and then down the pipe in the direction of the thread (snugly) until you hit the end while overlapping 50%. Done!

  22. Steve

    Another small point. Usually the tape roll gets moved around the thread. There are two ways to hold it. One way unwraps tape from the roll with each wrap. The other wraps tape onto the roll unless you allow it to revolve in your hand. Counter intuitively, the latter is usually the best way to do it with a finger through the hole in the roll and thumb acting as a brake.

    Otherwise the roll of tape, which often has a larger diameter than the workpiece, gets further and further away from the job. This is a pain in a confined space, and the increasing distance makes it difficult to wrap accurately.

  23. NPT Fitting | Sealing NPT Threads | Fire Hose Supply

    […] Teflon tape is a non-adhesive tape made out of Teflon that fills the gaps between the threads on the fitting and the pipe and locks them in place. It is more commonly used when the piping will be used to carry gases such as propane. […]

  24. Steve

    After having installed the hot water tank and have use teflon tape on both pipe joints, some weeping has begun. My question is will the weeping eventually stop or should I redo it with pipe dope???