Through-Bolting Ski Boot Heel Tech Fitting

Post by blogger | April 12, 2013      

Bucolic whine of the cordless drills, could life ever be better? Dove in on this one, check it out.

Through bolt project for boot heel tech fittings.

Through-bolt project for boot heel tech fittings. Click images to enlarge.

Some boots have a hollowed out area in the heel where it’s easy to nut the end of a bolt inserted through the rear tech fittings. In my experiments an 8-32 x 1 inch machine screw nested perfectly into the tech fitting, but unless sourced from the best quality supplier seemed a bit thin for truly beefing things. Instead, I used a 10-24 x 1 inch, and after installation I filed the head down nearly flush with the fitting. This removes the zinc coating, so when you’re done spray or paint the filed areas with a bit of lacquer and watch for rust during service. When doing the final install, everything should be bedded in a strong epoxy such as JB to seal against moisture and prevent micro-movement.

To fit the 8-32 screw through the fitting, it was necessary to ream the hole a small amount. I did so to the point of still having a tight fit that required threading the screw through the hole, rather than easily pushing it. Idea is that all gaps and tolerances in this project need to be minimal. Be advised that the tech heel fitting is hardened steel, you can’t just pop a cheapo drill bit through the hole. I reamed by using a tight fitting drill bit and angling the bit while spinning.

As for drilling the hole in the boot, this was drilled tight. I then threaded in the bolt and over-tightened so it stripped and turned to accept the nut. That way the hole was the most minimal diameter possible. Driving or pressing the bolt through the hole for a press-fit could be an even better option. Whatever you do, again, the goal is zero possibility of movement.

Looking inside, nut and screw have been tightened.

Looking inside, nut and screw have been tightened. I cut off the screw slightly too short, which wasn't necessary. Using a full 1-inch would have been ideal and protruded a few threads.

Looking from the outside.

Looking from the outside. The 10-24 screw head protrudes a bit from the countersink. This was filed down nearly flush then protected from corrosion. For the tech binding heel gap to work correctly it's important the screw head be flush or nearly so.

Again, epoxy should be applied to all surfaces to lock threads, prevent micro-movement, and seal against hidden corrosion. Use common sense and experience to apply correct torque to the screw and nut.

Note that using an 8-32 screw results in a smaller hole bored in the boot, and sits nicely flush in the fitting counter-sink. For average skiers this could be a better size bolt for the mod. This especially true considering the main purpose of this project is to get rid of the stock screw which numerous reports indicate loosens or breaks. I used the larger 10/24 in this how-to to show the maximum way this mod could be configured. In the end, anything is better than what is essentially the thin un-locked wood screw that holds most boot heel tech fittings. My seat-of-pants engineering sense tells me to use regular hardware store (around grade 3) hardness fasteners for this mod, as they’ll be more resistant to fatigue cracking than hardened fasteners. That is just an assumption, perhaps using hardened fasteners would be better. Corrosion is probably a bigger issue, though hardware store fasteners may be unreliable in terms of steel quality. Seal everything well.

If you’re considering this mod after you’ve sheared off the stock screw, your first challenge will be getting the broken screw out of the boot. WildSnow readers report that using a left hand drill bit can extract the broken screw. It’s possible you could also drive the broken screw out in the forward direction with a pin punch, since you’ll be drilling a through-hole anyway. Perhaps heat the broken screw first with the butt of a backwards inserted drill bit.

Which brands and models of boots accept this mod? Unknown, but easy to evaluate by pulling heel pad out of shell and examining the area where the bolt would seat. Installing a custom shaped washer under the nut might be a good idea for maximum strength. To re-glue heel pad in boot, use a dab of silicon caulk.

WildSnow “wax iron” difficulty rating: 3 out of a max 5 wax irons — 5 being most difficult.

If you’re concerned about your tech boot heel fittings but don’t need or desire this complex a mod, consider at least removing the tech fittings and bedding in epoxy. Check this link for that.

(Disclaimer: This is an experimental modification and has not been extensively tested for durability.)


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38 Responses to “Through-Bolting Ski Boot Heel Tech Fitting”

  1. Erik April 12th, 2013 9:17 am

    For shearing problems, try a solid shank structural aircraft fastener. It’s the thread root at the head that will get you. Look for base part number MS24694 with code C for stainless. You can get them from Aircraft Spruce or WicksAircraft just to mention a few online sources. Emphasis on the nylok nut, good call.

  2. Lou Dawson April 12th, 2013 10:18 am

    Erick, please go ahead and share a link for aircraft quality 10/24 x 1 stainless flat head machine screw, likewise for 8/32

    How strong is the aircraft stainless in comparison to grade 3 hardware store machine screw?

  3. Dave April 12th, 2013 10:23 am

    There threaded self tapping inserts designed specifically for plastic. These could be used on boots without a heel pocket or as a field repair.. Check out Dodge or Helicoil ( These aren’t common hardware store items but should be readily available at industrial fastener suppliers.

  4. Bill April 12th, 2013 10:30 am
  5. Lou Dawson April 12th, 2013 10:35 am

    Um, this is starting to get fun.

  6. Lou Dawson April 12th, 2013 10:51 am

    I just ordered a selection of Ti flathead machine screws to do this as permanent mod on some of my boots. I think the 10-24 hardware store option is probably ok, but hard to know for sure. Advantage of Ti is I’m pretty sure the 8-32 will be plenty strong, corrosion resistant, etc.

    I might be able to do a seat-of-pants test on how much stronger the Ti screws are over the hardware store mystery screws. Stay tuned.


  7. Lou Dawson April 12th, 2013 10:59 am

    Dave, I’m pretty sure that using inserts in the boot heel hole would result in way too big a hole and possible weakening of the boot. If the boot doesn’t have an open area for the through bolt, best upgrade would probably simply be purchasing stronger flathead screws such as the Ti, and reinstalling everything with JBweld per my previous post.

    Quite a few boots allow access from inside for a through-bolt. I just checked some Scarpa Maestrale and they have access (I can even see the end of the wood screw protruding into the inside of the boot.)

    Interestingly, the Maestrale RS has a Scarpa branded fastener in the heel fitting, I’m assuming they’re doing this so they can use a proprietary fastener that’s strong and quality controlled. More evidence that attaching the heel fitting with this one tiny screw is a bit marginal for some skiers…


  8. Ben April 12th, 2013 11:57 am

    IMO titanium screws are not stronger than high-grade steel screws; at best comparable to mild steel and some grades of stainless. I don’t think I agree that mild chromed steel is going to be more reliable than a high grade machine screw. If you look at parts that are subject to a lot of fatigue cycles and have a constrained diameter, so you can’t make them super fat – my experience is with bicycle parts – they tend to be made out of high grade steel. Examples from the bicycle world include traditional bottom bracket spindles, hub axles, pedal spindles. Ti pedal spindles exist but they have weight limits, and people break them. Fastenal and similar places should have a decent selection of stainless and high grade screws.

  9. Lou Dawson April 12th, 2013 12:06 pm

    Thanks Ben, that’s some good thinking. My idea is that the Ti won’t rust, if the steel screws get any corrosion they’e weaken quickly. Boots are rust factories, always moist inside, etc. But I’ll probably fool around with some grade 8 screws as well, they’re sure cheaper than the Ti!

    But, the Ti is lighter (grin).


  10. Greg April 12th, 2013 12:40 pm

    I’m with Bill on the insert (Helicoil would be my choice, but only because I have experience with them). The main advantage I would see is that you could do an installation with a helicoil that doesn’t punch a hole through to the inside of the boot where all the sweat is, and should be able to greatly reduce the risk of rust (getting good stainless steel fasteners would do that as well).

    I’d probably go with the 8-32 stainless steel screw, in the same length as the wood screw that you’re removing, I’d guess around a 5/8″. Then I’d get a helicoil, probably in the 3/8″ length. Drill your hole for the helicoil, being careful not to punch through to the inside of the boot. Install the helicoil and screw, possibly with some loctite to make sure it stays in there. Maybe put some epoxy around the top like you said to help keep moisture out.

  11. Greg April 12th, 2013 12:43 pm

    Oops, and by “Bill” I meant Dave.

  12. John Gloor April 12th, 2013 3:17 pm

    I have a BD boot with molded in fittings, so this is moot to me. If I were to do this, I would have more faith in a through bolted mod like Lou did as opposed to an insert or helicoil. In a binding mounting comparison, a t-nut is the strongest mount and is comparable to the nylock inside the boot.

    As a big guy, I have always shied away from light weight solutions for critical pieces. On a bike, I would never go with a Ti axled pedal over chrome-moly steel. lighter people get away with that though.

  13. RobinB April 12th, 2013 3:44 pm

    By 8/32, I assume you mean 8-32, not 1/4″?

    If one wanted to try the insert route, the Binding freedom inserts accept an M5 screw, which is just a few hairs over the size of the 10-24 machine screw.

    Obviously there is a problem, as people report shearing the screws in use. However my guess is that the screw’s main function is to hold the fitting snug to the back of the boot so that the two pins can take the load. There should be no extra tension load on the screw in normal use. I would bet that a regular check of the snugness of the screw would go a long way to preventing issues. Or gluing the screw in as suggested.

  14. Lou Dawson April 12th, 2013 4:46 pm

    Robin, thanks for that, I wrote those incorrectly. it’s a #8 screw, I’ll correct. Thanks, Lou

  15. Erik April 12th, 2013 8:03 pm

    I think Ben is on the right train of thought. I tend to avoid general purpose Ti fasteners because they aren’t very well controlled and you generally can only guess what heat treatment level and therefore strength and “brittleness” you’re getting.

    The solid shank fastener would have somewhere in the ballpark of twice the real world strength compared to fully threaded after some use. Nothing really to do with the material so much as the notch sensitivity… similar to ripping open a plastic bag being at the “tear here” notch.

    That link will get you to the spot for the solid shanks fasteners, scroll down to find the thread and length which is desired, they come in 8-32 and 10-32. I assume you would want a 29/32 length. I would probably use one of those in stainless and a stainless nylock.

  16. Bar Barrique April 12th, 2013 9:30 pm

    Good Post; I haven’t had a major failure with my boots yet, but if I do I now have a solution.
    Three irons difficulty, mine is the “laundry” type.

  17. Bill April 13th, 2013 9:35 am

    Hey Lou

    Be careful with the titanium or stainless.
    Make sure you use some kind of lube on the threads.
    If a stainless nut is used they can seize real easy by galling.
    Both titanium and stainless have very good fatigue resistance.
    The titanium is more springy, but plenty strong for this ap.
    and stronger than the typical hardware store screw as
    you picked up.

  18. Lou Dawson April 13th, 2013 9:43 am

    Thanks Bill, I’ll be using titanium as it seems to be the best combo of strength and corrosion resistance, but with regular or stainless steel nut to save money. Everything will be sealed and lubed. Lou

  19. Scooter April 13th, 2013 3:15 pm

    This is certainly a great repair option if you have had an issue with the oem attachment of the heel plate. Just an FYI though…. True for almost every gear company out there, any mods will void warranty, though I would assume most would warranty a shell with this mod that has a crack in the overlap on the instep. Any issues with the heel would give the gear company more leverage. A mod like this is a Dynafit’s lawyers dream if an injury claim was brought against them by the user. Buckle mods, shell fitting mods are all great, but when a user messes around with the boot/binding interface surfaces the injury liability is placed on whomever (personal or shop) did the mods.
    I will certainly do this mod if I ever have an issue with my boot, but I think it is important for those doing this to know what they are getting themselves into.

  20. Lou Dawson April 13th, 2013 3:26 pm

    Scooter, all that always bears repeating. Thanks, Lou

  21. Bar Barrique April 13th, 2013 10:26 pm

    I live in Canada, and, I’m not familiar with credit cards south of the border, but my Canadian Visa card gives the user a 1 year warranty extension in most cases when it is used for purchases. So when I’m buying “breakable” type stuff, I take advantage of this extra insurance.
    Having said that, sometimes we have to take risks, and, accept the potential liabilities.

  22. Bill April 14th, 2013 8:29 am

    Hey Lou
    Any way you can grind a fender washer down or drill a hole in some steel to fit under the nylock nut?
    I am just thinking the plastic is going to compress under the head of
    the nut and could use more area to support the load.

  23. John Monette April 14th, 2013 8:30 am

    After reading about this projec and relying upon my 30 plus years as a skier and as a master electrician.
    the solution to your issue is that you sjould use a stainless steel fastening system.iit does not corrode nor rust.and is soft so there should be no problems with for the sealant issue,use of a rtv sealer would be sufficient as well as to seal the entrance hole.
    also RTV would allwo for slight give in the assembly,again so as not to fatigue the heel of the boot.
    In past years I have suffered the indignaty of having to ski down the mountain with the heel of the boot blown apart……………….Not a great feeling …….Also not great stability in the process of getting down the hill.

  24. Lou Dawson April 14th, 2013 8:44 am

    Bill, I think in final projects I’ll make a washer. It does sound like stainless steel will be fine, I already ordered up the titanium so that’ll be first. Thing is, the bolt does not require a lot of torque and the boot heel fitting does not undergo a lot of forward and backward force, it’s more of a shearing up/down force the screw or bolt is resisting, and don’t forget that the boot heel fitting has the two pins that insert into the boot plastic as well. Lou

  25. Dave Field April 15th, 2013 8:39 am

    I like it, especially the nylock nut. Sounds like using a fastener with a solid shank behind the head to resist the shear and a snug fit through the plastic and you’re back in business!

  26. Lou Dawson April 15th, 2013 9:00 am

    Dave, I looked at the typical stock “wood screw” fastener again, and even the smaller machine screw is obviously stronger. I’m not sure using the solid shank fastener is that important over just upgrading to an 8-32 machine screw, through bolted with everything bedded in epoxy. Lou

  27. dgg April 15th, 2013 12:10 pm

    FYI. The screws that come in the boots for holding the insert in are a far cry from a woodscrew that you would buy at a hardware store. For the most part they are alloy steel and coated in away that minimizes the effect of corrosion on the base metal, even with the inevitable coating damage that occurs. The threads in the plastic may be a weakness with many installations but the screw itself is not.
    A typical stainless screw as a replacement is not adequate in the cyclic loads this sees whether it is a machine screw or not.

  28. john nobil April 15th, 2013 1:20 pm

    ah back to boot mods, a source of great creative experimentation in the ski shop/man cave when the nights are long and the women are lonely. my latest tlt5 upgrade: replace the flimsy stock tongues with the much burlier vulcan tongues, a very easy way to step up the forward lean resistance of the boot. flex those vulcan tongues, they feel about 3x stiffer than stock tlt5’s. all that is required is a slight modification. drill and cut a new square hole so tongue locks into the tlt5 square peg properly. when the lady starts sending after closing hours messages about why you’re home late again, tell her “I’m bringing vulcan tongues” 😉

  29. Lou Dawson April 15th, 2013 2:23 pm

    dgg, reality bites, people are having those screws break…. I agree they are not “wood screws” but they are weak in comparison with the rest of the system. The binding release should be the fuse, not breakage. Lou

  30. Lou Dawson April 15th, 2013 2:24 pm

    John, I’ll try your tip (grin). Lou

  31. dgg April 15th, 2013 2:51 pm

    Sorry in reality the original post doesn’t mention why the replacement was required. So I was just trying to help address some of the assumptions stated in the original post. I suggest the manufacturers (for sure BD, Dynafit, and Scarpa) have done a good bit of testing on these screws and in a new boot with good threads the plastic screw interface is not the weak link. When the screw comes loose the cyclic load can cause the head to break off. Of course the screw hole in the plastic is damaged then yes the through bolt or threaded insert may be necessary, otherwise a replacement screw from the boot manufacturer is likely a better bet. The range of quality in grade 3 hardware screws is vast and in cyclic fatigue loading scenarios it can be a real gamble. If you are through bolting or using a machine insert buy the best screw you can find which may be your Ti piece or a coated grade 9 SAE or 12.9 metric.

  32. Lou Dawson April 15th, 2013 3:00 pm

    Dgg, that’s a good point. I was responding to quite a few comments over the past few years when people have shared about fittings breaking off due to the screw shearing. I did write “If you’re considering this mod after you’ve sheared off the stock screw, your first …” But I could have been more clear. So I’m hear to say, “the fitting screws break, here is a possible solution.” And indeed, if a person does this mod I now totally agree the screw should be something higher quality than hardware store grade “3” garbage. I think the Ti stuff I ordered will fit the bill.

    Also know that if the fitting breaks off, it could cause life threatening consequences, so I’d suggest that until I cease hearing stories of broken fitting screws, mods such as I’m suggesting might be wise if done well by an experienced mechanic and ski boot worker. I would caution folks to NOT do this sort of mod unless you’re an experienced craftsman and you use high-quality hardware.

    As for companies testing, who knows. There is no DIN/ISO standard so doing so is totally optional, and to what standards they’d test is just guesswork. Don’t have so much faith in corporations, even if they make ski gear (grin), aren’t corporations the root of all evil (grin)? Or is that just Walmart?


  33. Bar Barrique April 15th, 2013 8:45 pm

    While I think it is a good idea to use quality fasteners, it seems that the breakage occurs when the screw comes loose. When the fastener is tight the plastic “shelf” on the boot bears the load.

  34. Lou Dawson April 16th, 2013 7:20 am

    Bar, I think there is a good chance you are correct, my gut feeling is that through bolting will totally eliminate fastener breakage simply because it will never come loose — but making it stronger than stock seems like a good idea as well, since it’s easy to do so. Bedding everything in JBweld is also key, in my opinion. Lou

  35. Coz April 19th, 2014 12:09 pm

    Sorry to bring back up a an old thread, but I’m trying to problem solve. I had the screw on my 3 yr old Maestrales break a few weeks ago. It seems the breakage was from where the heel of my boot hit the heel post of my Sportiva RT bindings – my skis are soft and the ski bent when spanned over a gap. The hit was enough to break the wood screw AND one of the two inserts molded into the tech heel piece itself (I think this must have been happening more often than I realized because of some extra girth around my middle in the last year).

    I have a replacement tech fitting from Scarpa, but I’m having a hell of a time getting the screw and post fragments out of the holes. I have broken three bits trying to drill out the fragments, including one left handed bit. Now I’m thinking about trying to access the holes from the inside of the boot so I can push the fragments in and then through-bolt. Has anyone else done this? Anything I should be worried about if I proceed?

  36. Lou Dawson April 19th, 2014 1:35 pm

    Yes, you should definitely just through-bolt it. I’d think if you were ultra careful you could get the screw shaft out one way or another, but the post frags sound like another matter. Perhaps take the boot to your friend who runs the MRI machine and pull them out with the magnet (grin)? Seriously, you could have an insurmountable problem. I’d probably attempt to drill a small hole from the inside of the boot, then push the frags out with a small diameter straight pick, or reversed drill bit. Problem is, how to know where to drill? Perhaps shine a bright light on the outside of the boot heel and see if enough light comes through the plastic to indicate where the frags are. Come to think of it, if you could do this for the screw you could perhaps just drive it back out with a small punch. Indeed, the heel fitting is a very hard steel, you’re not going to be drilling out those broken posts.

    Another idea about the broken posts, just drive them farther in to the boot with a small punch, or even place the new fitting over them and do some light pounding, using the new fitting to push the old parts deeper.

    Bed the new fitting in JBweld for sure, and figure out ways to prevent corrosion.


  37. Coz April 20th, 2014 2:48 pm

    Thanks, Lou. I like the idea of trying to push the posts back out by punching through from the inside of the boot. I won’t have much room to swing the hammer, but I think I want measured taps anyway. With the bright orange Maestales, it’s actually not hard at all to see the studs – the material is fairly transparent. And I will epoxy the hell out of the finished product if I can get these studs out – and the fitting on the other boot as well.

    And your joke about the MRI machine isn’t far off! I have a friend who is a post-doc engineer at a big-name university, and he agreed to help me out in the lab next week. I wonder what kind of fun toys he will let me use…

  38. Lou Dawson April 20th, 2014 2:52 pm

    There are magnets that could easily pull those pins out..

    As for pushing out, I think you could use a sharp straight pick and just push through the boot plastic from the inside. Warm the boot up first.


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