Today I’m showing you how I use threaded inserts in wood. Threaded insert nuts also sometimes get called ‘nutserts’ or just insert nuts and are a very handy way of using a threaded machine screw or bolt in wood.
You can watch the tip video here:
What are threaded inserts?
Threaded inserts are a clever little invention with a coarse wood screw thread on the outside an a fine machine screw thread on the inside. It effectively allows you to use machine screws in wood and are invaluable for any item where you might want to remove the screw at a later date. With a traditional wood screw, every time you remove the screw it damages the thread it cut in to the wood. Eventually the thread will disappear completely and you’ll no longer be able to use a wood screw in that hole. A better solution is to use threaded machine screws and used in conjunction with threaded inserts this is a relatively simple process.
How to use threaded inserts?
With the insert nuts I’m using in the video, these have an outside smaller diameter of around 8.5mm. For something like this a 9mm pilot hole should be fine. You can even get away with 8mm in softwoods for a really tight fitting. Always follow the manufacturer’s recommendations for the pilot hole size. You can use a depth-stop on the drill to help with the drilling depth -- this is particularly handy if you have a lot of them to fit.
Fitting the screw in the hole can be tricky. Some have an in-built hex socket. So have a slot designed for flat blade screwdrivers. An easier solution is to use the machine screw you plan to use in the final fitting and attach a locking nut to prevent it from turning. You can then use an impact driver to fully drive the insert nut home. Loosen the locking nut with a small spanner and you can then remove your machine screw. This is also the method you can use on unheaded threaded inserts.
I prefer to use carbon steel insert nuts are they’re robust and very unlikely to break. Obviously if the fitting will be subject to any dampness make sure you use corrosion resistant nuts. You can get brass insert nuts but generally these are only suitable for very soft materials otherwise there’s a reasonable chance they will break on insertion.
Which way up do threaded inserts go?
There’s a bit of an urban myth out there that slot-head inserts should be installed upside down since the slot is design to ‘cut’ the thread in the wood. This, for the most part, is incorrect. No idea where the rumour started, perhaps there are brands out there that are specifically designed to go upside down, however in most cases the slot is most definitely designed for a slot head screwdriver. Here’s confirmation, images courtesy of shop4fasteners.co.uk:
There are other types of threaded inserts designed for metal and plastic where the cut-out goes to the bottom. These have a slightly tapered design and a much finer thread pitch. These can only be installed using a threaded mandrel or using the method shown in my vid:
No idea if that’s what’s been causing the confusion -- if you know different pop a pic on Instagram and let me know! Obviously if you want to install them upside down that’s entirely up to you. Threaded inserts and a great, cheap fixing to have in your arsenal if you’re ever making anything that might need to be taken to bits at a later date -- hope you found this useful! Remember you can find a list of a lot of the products and tools I use here if you’re in the UK and here if you’re in the US.