WildSnow Technical — Binding Mount Screw Length


Post by WildSnow.com blogger | June 6, 2016      
Many ski touring bindings use different length screws for the toe and heel units, if you're not paying attention it's possible to use the wrong screws. Example being the use of heel screws in this Vipec toe, resulting in barely two threads engaging the ski.

MISTAKE! Many ski touring bindings use different length screws for the toe and heel units, if you’re not paying attention it’s possible to use the wrong screws. Example being the use of heel screws in this Vipec toe, resulting in barely two threads engaging the ski. Key is to evaluate all screw lengths before you begin a mount. Keep a clean and well organized workbench so you don’t grab the wrong screws during the process, as once the binding is on the ski and you can’t see how far the screws are inserting.

The other day… a misfortunate soul I chance encountered at a trailhead had to ski out of the wild on one plank. The binding had popped off the ski like a champagne cork during your 2nd wedding anniversary. I got a quick look at the culprits. Not sure what truly went wrong, but the toe unit screws had about two threads engaging the ski. Suspicion is the mounting tech fired the shorter heel screws into the toe, or, just picked up random screws of the workbench. Whatever. Inspiration for a blog post.

Thing is, I realized we needed more exposition here on Wildsnow about binding screw length for those of you doing home mounts (and perhaps for shop employees as well?). More, I’m realizing that some of the binding pull-outs we’ve heard of over the years could well have been caused by improper screw length. I’ll add links to the post to all our home mount DIYs, check it out.

Normal protrusion  of a ski binding screw is about 7 millimeters.

Normal protrusion of a ski binding screw is about 7 millimeters. BUT, always measure thickness of the ski and compare to the screws, some thinner skis require shorter screws.

Using screws that are too long is a common mistake.

Using screws that are too long is a common mistake. Sometimes doing so has no consequences, but you run the risk of damaging the ski if the screw presses against the base laminations, causing a “pimple” or blowing the layers apart.

Modern skis often include information about  what size hole to drill.

Modern skis often include information about what size hole to drill. In this case, 3.6 mm diameter hole that’s 9.5 mm deep, commonly provided by dedicated ski mounting drill bits. Most of the time I use my 7.5 mm length bits, presumably the Volkl 9.5 spec is specific for mounting Kingpins as the Kingpin rear unit screws insert about 8 mm into the ski. It’s said that a CE regulation requires all skis sold in the EU to have this information printed on the ski, but we’re not seeing that so who knows…

Always measure ski thickness in the binding mount areas, and compare to screw lengths.

Always measure ski thickness in the binding mount areas, and compare to screw lengths. In this case, a 7 mm screw insertion still allows for 4.5 mm of ski base layers, which is plenty. At a minimum I’d be sure your screw length allows for a couple of millimeters of material, as in the case of very thin skis. Shortening screws is easy but has to be done correctly. Don’t just blunt the ends, first shorten with a grinder, then slightly sharpen the end so the screws threads can ‘lead’ it into the hole without requiring excessive downward force on your screwdriver.

Dedicated ski drill bits.  3.6 x 9 at top, 4.1 x 9.5 at bottom.

Dedicated ski drill bits. 3.6 x 9 at top, 4.1 x 9.5 at bottom. The 4.1 mm bit is used for skis with metal topskin. In my experience, if you don’t have a dedicated bit you can use a 5/32 inch (3.9 mm) twist drill bit to drill both non-metallic and metallic (with a depth stop and care with how much force you apply). It’s also possible to use a slightly smaller 9/64 inch (3.5 mm) bit in non-metallic skis, but starting screws or tap in this size hole can be tricky. Use epoxy with all mounts, and tighten the screws with care so as not to strip. Reality is that the “standard” bit diameters are just an average of what works ideally for different types of ski construction, so slightly varying the hole size is not a big deal. We’ve been doing so for years with no problems. More information about thread tapping skis for binding mounting.

Blizzard ski mounting info.

Blizzard drilling info calls for a wider 4.1 mm diameter hole. The numeral “9” probably refers to maximum depth, as a 9 mm deep hole would be unnecessary for a screw only inserting 7 mm. In all, a good example of why you need to evaluate every factor specific to a given binding and ski mounting combination. Interestingly, the “max. 49 mm” spec refers to the maximum of how far apart your bindings screws should be, left to right.

IMPORTANT,  most ski touring bindings use different screws at the toe and heel.

Again, IMPORTANT, most ski touring bindings use different screws at the toe and heel. A good example is Vipec, which uses a fairly long panhead at the toe, and a shorter tapered head screw at the heel. Sort everything out before you begin.



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Comments

33 Responses to “WildSnow Technical — Binding Mount Screw Length”

  1. Bruno Schull June 6th, 2016 10:58 am

    Great info. Let’s say you put some epoxy or glue into the holes. Do you ever run into problems with the glue getting “stuck” or trapped in the bottom of the hole, pressing down, and creating a dimple or bulge on the base? Is is best to use a minimal amount of glue? Thanks.

  2. Lou Dawson 2 June 6th, 2016 11:08 am

    Hi Bruno, I’ve never had a problem with that unless I used screws that were too long. The screw threads probably don’t seal perfectly and often the ski core is somewhat porous. Nonetheless I’d think it would be wise not to just pump the holes completely full of glue, instead, use a few drops or work some into the hole with a tool like a thin drill bit. It’s also a good idea to inspect the bottom of the ski after your first screw goes in to make sure you didn’t mess up. I’ve made a lot of mistakes with screw lengths being too long, when I was in a hurry. Lou

  3. John J June 7th, 2016 10:17 am

    I would think that if my binding screws were 490mm apart, side to side, at least one of them would be off the edge of the ski 😉

    I notice that the Blizzard ski has the weight/area printed on the topsheet also. Could they be following a trend started by WildSnow?

  4. Thom Mackris June 7th, 2016 3:43 pm

    For users of Binding Freedom / Quiver Killer inserts, know that you’ll get full screw strength with a binding screw that engages at least 3 threads of the insert. Of course, if you can get more without bottoming out in the insert, that’s great!

    Naturally, you want to install the insert flush with the top of the ski, with the caveats about no dimpling your base.

    Cheers,
    Thom

  5. brad June 9th, 2016 11:15 am

    I also had a toe piece inexplicably pop off while touring this winter. My partner had two hose clamps similar to this:
    http://www.grizzly.com/products/4-Hose-Clamp/W1022?utm_campaign=zPage
    We put the toe piece back in holes, one clamp in front and one behind, and I was still skiing!
    So now two hose clamps will (hopefully) consume weight in my pack for the rest of my life.

  6. Lou Dawson 2 June 9th, 2016 12:17 pm

    Brad, did you ever figure out why the toe failed? Lou

  7. brad June 9th, 2016 1:56 pm

    I had the toe pieces replaced about 3 years ago as some sort of recall per Dynafit. Since I live close to the Dynafit shop in Boulder, I brought them in to have them do it. Apparently when the Dynafit shop tech installed the new toe pieces he didn’t use glue, so water got in the holes and rotted the boards. (This is according to a different and very experienced ski tech who would later inspect and fix them with large heli coils)

    Point is that, although rare, there are several reasons a toe piece could pull off, and when it does there is little or no warning. Those little hose clamps saved the day.

  8. Lou Dawson 2 June 9th, 2016 4:29 pm

    Yeah, it is so so important to use glue, preferably good quality epoxy. Lou

  9. Knut June 11th, 2016 3:17 am

    Excellent advice piece! Thank you once more, wildsnow is really a place of an unrivalled collection of knowledge around everything binding you to your skis.

    Just one comment: I am pretty certain the 490mm info on the Blizzard relates to the length of the mounting area along the ski’s axis. So how far the foreward mounting holes can be away from last screws in the tail’s direction. Which would also mean 245mm in each direction from the mid sole mark.

  10. Lou Dawson 2 June 11th, 2016 7:14 am

    Knut, thanks, that might very well be the case with the “490.” I recalled someone talking to me about binding screw width spacing, but they could have been mistaken as well. On the other hand, 245 mm in each direction from the mid-sole mark on ski is immense… Lou

  11. Sedgesprite June 11th, 2016 10:57 am

    On the quiverkiller mounts: Wouldn’t a slightly ‘proud’ mount, (threads just barely above flush), offer more clamping force and a better grip between ski and binding?

  12. Lou Dawson 2 June 11th, 2016 11:40 am

    NO! The binding needs to sit firm on the ski. If anything, a slightly dimpled mount would be better than a proud mount. It’s also wise to consider some industrial double sided carpet tape between the ski and the binding. And most certainly between the binding and any shim plates. Lou

  13. Phil June 11th, 2016 12:29 pm

    Interesting – I’ve never used or heard of using 2-sided tape in a binding mount. Can you expand/ on that a bit more? Obviously it would produce lots of friction that could help if a bolt loosened. Any more comments or efficacy info?

  14. Knut June 11th, 2016 4:41 pm

    Hi Lou.
    Actually, it is not that immense, when you consider that some bindings, especially frame bindings are pretty long. The Fritschi Freeride Pro in size XL for example is approx. 480mm from the foremost to the backmost screw holes. That leaves you just with 5mm wiggle room in both directions to change mounting position.

  15. Lou Dawson 2 September 13th, 2016 8:01 am

    Phil, in some cases it’s obvious that shear forces on the binding (forward-back-left-right) are only resisted by the tension of the screws, especially in the case of things such as Quiver Killer, due to the screw diameter being smaller than the holes in the binding mount plate. That can be ok, but in our view adding the added insurance of something like double sided carpet tape can be wise — especially in the case of stacking binding plates and shims to raise height of toe or heel. BUT, doing so is not a substitute for properly tightened fasteners!

    In the case of a “permanent” binding mount using OEM screws and epoxy, you can do the same thing by roughing up the ski top surface under the binding, as well as the underside of the binding plate, and adding a bit of extra epoxy under there so that it squeezes and spreads around the screws as you tighten down the binding on the ski.

    In the case of either epoxy or double sided tape, application of heat is your friend if removal is necessary…

    Lou

  16. Simon January 6th, 2017 4:47 pm

    Hi Lou, I’m about to home mount Dynafit Superlight bindings on Zag Adret skis using your brilliant paper template. The skis seem pretty thin to me at only 12.5 mm thick in the mounting area. Do you think I’ll be ok using the screws provided with the Superlights which will penetrate 9mm into the ski or should I be using shorter screws?

  17. Lou Dawson 2 January 6th, 2017 4:56 pm

    That’s thin. I suspect you might need to shorten the screws a bit. Any ski company worth beans should have specifications as to how deep the binding mount screws should penetrate. Can you get that for the Zags? I’d advise trying to get the information, instead of guessing. I’ve made too many mistakes myself in this regard…

    Also, some skis have the recommended screw penetration length printed right there on the top of the ski, perhaps Zag has that?

    Lou

  18. Simon January 6th, 2017 11:58 pm

    Thanks Lou, The info re screw depth isn’t on the ski and Zag never replied to my enquiry but I shall try again. P.S that was my first comment on your site, although it’s always the first place I go to when I’m in a fix..I love it!!

  19. See January 7th, 2017 8:47 am

    Seems to me that light touring skis with low density cores usually have some sort of screw retention plate in the deck, so I wonder if using the longest possible screws is really that important, especially with epoxy.

  20. Dan January 7th, 2017 12:35 pm

    The devil is always in the details. With that in mind Lou, when heating the binding screws (epoxied) to assist in removal, how much heat is needed and approx. for how long? A 30 watt soldering iron? 100 watt?

    Thanks in advance.

  21. Lou Dawson 2 January 7th, 2017 3:37 pm

    There is no way to standardize, it’s done by craftsman instinct. If you want, glue a screw into a puddle of expoxy then heat the screw with your soldering iron and see how long it takes… I can tell you it’s not a lengthy procedure, I usually try 20 seconds on the first one. Using a hand screwdriver you can tell if you’ve softened the epoxy enough, if not, give it another 10. Risk is in melting the binding plate plastic under the screw head, so if in doubt try 15 seconds on the first one. Lou

  22. Stan January 25th, 2017 6:11 am

    Hi Lou, first of all, thank you for you insightful info, it is very helpful!

    I am about to mount ( first ever mount ) my Marker Kingpin 13s to my Blizzard zero G 95s and I have three questions:

    1. Since I live in Europe, we do not have odd bit sizes such as 3.9 or 4.1mm. The screws provided with the bindings are 5.5mm self-tapping screws that will go in around 7.5mm into the skis. My question is, should I use 3.5 or 4mm drill bit for the pilot hole?

    2. I will be using extra strong 2 part epoxy which has to be applied within 4 minutes and solidifies in 3 hours? Is it ok to use this epoxy, or should I use an elastic epoxy ( not as rigid as the one I have)?

    3. Do I still need to tap the holes with a tapping tool, given the screws provided are self-tapping? (I do not have the correct gradient tapper)

    Thanks in advance! Stan

  23. Lou2 January 25th, 2017 6:57 am

    Hi Stan, you can probably use the 4 mm bit, and not tap the holes. What I would do is after you drill the holes, try starting a screw in one of the holes without the binding, just to figure out if the screw self-taps nice and easy without undue distortion of the ski as it goes in. Sometimes I do this in all the holes, just a few turns of the screw, instead of tapping.

    As for the “odd” 4.1 mm sizes for bits, those are standard ski drilling bits and are available in Europe. I would suggest acquiring them since the Zero G skis specifically state in writing on topskin to use the 4.1.

    Use the elastic epoxy. The strength of the epoxy is not a big deal, in fact, stronger epoxy that cracks is weaker over time than epoxy that flexes.

    In the case of Zero G, the glue mainly serves to seal the holes, care with torque of screws and such is more important to holding strength.

    Lou

  24. Lou2 January 25th, 2017 7:01 am

    EVERYONE, where does one buy ski drill bits in Europe? I’m battling Google trying to find them. Thanks, Lou

  25. wtofd January 25th, 2017 7:16 am

    http://www.skiequipmentuk.co.uk/shop/products/Wintersteiger_Ski_Binding_Drill_Bits.htm

    http://www.tesmasport.com/coaches/drill-bits-pole-keys

    Otherwise, I’d ask your contacts in Austria. Any guide or ski manufacturer should be able to give you more local options.

  26. Lou Dawson 2 January 25th, 2017 7:21 am

    Thanks Wtofd! I knew you guys over in the EU would come through!

    And Stan, where are you located that it’s so difficult to get the ski drill bits?

    Lou

  27. Stan January 25th, 2017 8:03 am

    Hi Lou, thanks for the prompt response!

    I live in Bulgaria. Things are done in their own way here! 😀 I can purchase 4.1mm online, but I am guessing it will take at least 15 days to arrive, and I want to ski this weekend. The difference is only 1mm, however if it necessary, I will wait for a special bit to arrive!

    What kind of torque would you suggest for tightening the screws?

    Noted about the glue. Will go for the elastic one! Noted about tapping!

    Thanks a bunch!

  28. Lou Dawson 2 January 25th, 2017 8:42 am

    I’m pretty sure you can drill with 4 mm instead of 4.1, but try a test screw before you just go crazy jamming all the screws in. Lou

  29. Andy Mason January 25th, 2017 9:44 am

    About half the small bits in the world are 3.5, and the other half are 3.6, so I agree that it’d be safe to use the 4.0s. And for length, I use 9 or 9.5 all the time, 7.5 are normally for kids’ skis.
    Andy

  30. BenL January 26th, 2017 1:44 pm

    Jon at Piste Office in the U.K. has bits available and lists 4.1mm, I’m sure he could mail to Bulgaria. Piste office.co.uk

  31. Andre November 10th, 2017 11:32 pm

    I second Stan’t question. Do you have any particular average torque setting you mount the bindings to? I did some very unofficial tests and figured that I can rotate the screwdriver at a fairly comfortable consistency up to 75 inch pounds. However, without doing a bunch of tests I’m rather nervous about the number.

    I have mounted Radicals 1.0 on Voile V6s at 65 inch pounds and didn’t have any issues with screws stripping.

    I have noticed that if I wait a few minutes and then re-torque, the screws will turn a little more before the click. As always I ramp up the torque. Meaning torque to 30 inch pounds first, then 45, then 65 and then double check the top number about 3 to 4 times until the clicks come without the screws turning at all.

  32. Andrei November 10th, 2017 11:51 pm

    After looking around, it seems that 65 inch pounds is about 7.34 or so Newton Meters and is potentially a bit too high. Numbers being bandied around are closer to 45 inch ponds. Any thoughts?

  33. Lou Dawson 2 November 11th, 2017 6:36 am

    What I tend to do is tighten a screw by hand, since I’ve got a feel for it, then use that screw to check and adjust settings on torque limiting screwdriver.

    Seems I end up at indeed around 45 inch pounds.

    Some screws can take quite a bit more torque than that, as when in a beefy metal topped ski, but even though a screw can take more torque doesn’t make it necessary. If the screw is tightened down and epoxied, then it’s done.

    https://www.wildsnow.com/22864/fat-torque-wrench-screwdriver-review/





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  • Welcome to Louis (Lou) Dawson's backcountry skiing information & opinion website. Lou's passion for the past 50 years has been alpinism, climbing, mountaineering and skiing -- along with all manner of outdoor recreation. He has authored numerous books and articles about ski touring and is well known as the first person to ski down all 54 of Colorado's 14,000-foot peaks, otherwise known as the Fourteeners! Books and free ski touring news and information here.

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