Back to a Slightly Flawed, Six-pronged Friend

6-prong_t-nut_IMG_0198

I have concluded that the surface-mounted tee-nuts (item 94122A200 from McMaster-Carr) are difficult to break, but they do break at the collar if you tighten their mating bolts too much.

So I removed these 14 tee-nuts from my knockdown Nicholson bench. When it comes to a workbench, nothing should be light- or medium-duty. I replaced them with an old standby for me: the six-prong steel tee-nut for wood, also from McMaster-Carr (90975A163).

These are less expensive – $13.72 for a pack of 50 – and can be tightened with prejudice. You’ll crush the wood before you strip or break these tee-nuts. The downside? They will sometimes fall out when your parts are disassembled.

And here ends the great surface-mounted tee-nut experiment of 2014.

Tomorrow I’ll finish up this workbench – flatten the benchtop and install the crochet. I’ll also shoot a video of how the bench knocks down for travel. I am pleased with the way it goes together.

Then I’ll get back on a pair of Roorkee chair commissions.

— Christopher Schwarz

About Chris Schwarz

Publisher of woodworking books and DVDs specializing in hand tool techniques.
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22 Responses to Back to a Slightly Flawed, Six-pronged Friend

  1. You could still use a couple pan head screws to secure the T-nut.

  2. Matthias Wandel uses the pronged T-nuts extensively and adds a screw to keep each from falling out. See http://www.woodgears.ca.

  3. steveschafer says:

    Bedding the T-nuts in a little bit of silicone caulk should keep them from falling out.

    • gyegreene says:

      Heh! I was going to suggest a similar approach: a blob of softened beeswax (which I find “tacky” rather than “slippery”).

      –GG

      • smbarnha says:

        A lot of beeswax is tacky because it has propolis (tree resin) or even small amounts of honey in it. Pure beeswax is not tacky at all.

  4. jenohdit says:

    Good ole steel. Those other things look like injection die cast zinc similar to Euro hinges. I love me some good quality Euro hinges but the lesser quality ones break just like those problem t-nuts.

    These guys will wear out and will strip. I’ve used them for bent laminations like Frid describes in one or more of his books and had to improvise on the fly mid-glue up when a few have striped out. Normal bench break down and set up probably won’t put that much load on them though.

    What I’ve never seen is them falling out of their holes though. I’ve always had the opposite problem. I can’t get them out easily when I want to. It seems the holes tighten up and they get stuck. I put a bolt in them from the other side and hammer them out.

    I’m not sure exactly where this Kentucky place is. If it’s the Southern hemisphere, then that explains a lot.
    ….
    I looked at the break and my thought was that it was as much due to torsion as to tension, so, right before hitting post, I went to Mc Master Carr and lo and behold the bad guys are zinc. The combination of pull and twist is harder to resist than pull alone since the load is going to be significantly increased. Lubrication would probably make them survive tightening but who want to remember to do that. Maybe a good waxing once.

    They are probably really good for their intended use, leveling feet whose load is directed along the axis rather than twisted. The screws would keep the feet from falling off of the bottom of whatever they are mounted on.

  5. noelhayward says:

    I was wonding why Chris did not use the pronged nut in the first place as they are cheap and easy to obtain.

  6. Matt Talley says:

    I have built 4 rock climbing walls using t-nuts to mount the holds to the plywood – two at large Southern California gyms – and t-Nuts being popped out was a huge pain in the a$$. I tried a little caulk, then some epoxy and in the end, I bought a box of 1/4″ Pan-head machine screws. I put a couple in at 12:00 and 6:00 using the prong made hole and with a little wax. Held like a champ – still holding 8 years later last I checked – and they get a lot of abuse from the kids who set new routes: torquing down the hold bolts, slamming bolts in the holes while in a hurry, etc. It is a little bit of work for serious piece of mind.

    • jenohdit says:

      I really don’t get how this problem occurs but it does seem to be an issue for some people. Don’t you put the t-nut on the back side of the plywood and bolt into it from the face side? How could the things falls off like that?

      • The T-nut falls out when things are disassembled, moved or stored. There isn’t much holding it in.

      • Matt Talley says:

        When the impatient youth put a hold on, they would often do it with the bolt in place and press it until the nut caught the threads. Sometimes this would mean that the t-nut was pushed out of the hole and would fall out of the plywood. Someone would have to go behind, find the thing, climb back up through the rear wall supports while holding a hammer and the t-nut. It was a pain and we kept finding hols where the less attentive route setters would not fixed tho popped t-nut and would put the hold somewhere else. after a while the floor behind was littered with hardware and it made route setting difficult.

      • jenohdit says:

        I see now. I learned a long time ago that climbing and me don’t mix so I know nothing about climbing walls. I didn’t know that the holds might get moved around.

        I have still never had to deal with one that I’ve put in coming out. I just drill a snug hole and drive them in. Maybe after a few expansion and contraction cycles they could fall out of solid wood. WIth engineered sheet goods I’ve had to slam on them from the other side to knock them out.

  7. In Tage Frid Teaches Woodworking Volume 3, the first project in there is a knock-down drafting desk he built for RISD. In there he embeds a t-nut into the end of dowel that is the same size as the flange and drilled out to accommodate the bolt you are using with the nut. Then drill a hole the diameter of the dowel into the piece you want to embed the t-nut&dowel. Insert and glue the t-nut&dowel (with the t-nut end going in first). I’ve found this method to be much stronger than trying to expoxy or screw down a t-nut as I’ve tried methods those as well in the past.
    -B

  8. rdwilkins says:

    Michael, you might try these T-nuts which work similarly but also have the holes for mounting screws. They’re made for climbing walls so they should be sturdy but I can’t promise they’ll stand up to your obviously powerful torquing strength. http://www.atomikclimbingholds.com/38-t-nut-round-base-with-brad-holes?gclid=Cj0KEQjwjtGfBRCN4-LU9ODG1-wBEiQAy_Xp7xlcx5ZosYV7rZGt4lFLq7wk2WelN1s2f6a1CeLX34UaAnxh8P8HAQ

  9. Have you seen these Nut Plates? Malleable iron sounds a lot more durable than cast zinc. http://www.mcmaster.com/#nut-plates/=td2ivc

  10. Aaron says:

    Umm…stupid question…why all this fuss about t-nuts at all. Seems like you have acces from the back to just add a nut and washer. Just a little extra hardware to keep track of when it’s broken down.

  11. Ralph Smoyer says:

    Have you considered using threaded inserts. They have great holding power. Drill the properly sized hole and and use a screw driver or allen wrench to thread the self tapping insert into the hole.

  12. Ralph Smoyer says:

    Threaded inserts from McMaster Carr 90016A031 or 90192A132

  13. Dean Morrell says:

    I work in a CNC shop working metal. It’s not what I love, but I learn more than I want about the stuff. The screw nuts from McMaster-Carr are zinc. Way too soft. The following are steel and likely just as strong as the bolt you are using. Same size threads too!

    Or find a list at this link:

    http://www.amazon.com/s/ref=sr_nr_p_n_feature_eleven_b_0?rh=n%3A16310091%2Cn%3A383599011%2Cn%3A16409861%2Cn%3A16410131%2Ck%3Abrad+hole%2Cp_n_feature_eleven_browse-bin%3A3622112011&keywords=brad+hole&ie=UTF8&qid=1408588088&rnid=3622110011

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