Main Description

Gibson®, Epiphone®, Stratocaster® and Strat® are registered trademarks of Fender Musical Instruments Corporation and Gibson Musical Instruments Corporation. Axesrus® has no affiliation with FMIC

Other Uses

As I've alluded to in the main section - #3 screws aren't JUST for Pickup rings, so, heres a few other places you may find them.

Screw Heads Explained

This is a little over arching, so i'll try and keep this brief. Screws come with different styles of head, we usually think of them as "Round head" or "Countersunk", but theres a little more to it then that. For the time being i'll just detail the most common ones you'll fine in wood screws.

Screw Gauges Explained

To be completely upfront - i am FAR from an expert when it comes to screw threads. I'm an electronics engineer by training, and a glorfied guitar tech by trade, so if your about to apply my logic to screws as a whole? It might be way off.

However - I've seen alot of guitar screws! So, if we're limiting this entirely to those? Heres how it works.

How it SHOULD work.

Screws, much like wire (where I’m much more comfortable!) are manufactured by either by “gauge” (which is based in the imperial system) OR in “Metric” – which is much simpler, but, weirdly, whilst it became the “norm” for machine screws (and bolts), it didn’t become the standard for wood screws.

So, right off the bat – we’ve got an important distinction here.

“Gauged Screws” first off – now, I know I said they were based in the imperial system! They are! But I’m not, so, you’ll have to excuse me working in millimetres for the most part. (I’ll include the common gauges in the Imperial Decimals and fractions)

There we go – need a wood screw? With a 2.4mm thread and a 4.8mm head? You need a number 3! It’ll likely be labelled as “#3 x 25mm”, or “No.3 x 1inch” – but it’s fairly straight forward. It’s a gauge 3 screw in whatever length.

Metric screws, are much simpler – usually displayed as M “number”, its as you expect. M1? 1mm diameter thread. M5? 5mm thread! M3.5? 3.5mm! You get the idea. And at the risk of insulting your intelligence, heres a table in the same style as the above.

Both systems go up into huge diameters too, but I’ll stop roughly within the realm of guitar parts!

*I’ve included the head size/spanner size column in the table, because it’s true, assuming you’re working with a hex head bolt… but, it is NOT true, or other head styles (so, based of the five different M3 screws/bolts I’ve got here, in different head styles? (Fillister, Hex socket cap, Round, Pan and Oval head) Theres 0.5mm variation across the range)

I’ve no idea why Metric screws didn’t standardised their head sizes in the same was Imperial/gauged screws did, but, there we have it.

So, without getting too bogged down in screws – as a rough and ready rule?

If your working with a “Proper Screw”? Something with a pointy end that going to be driven into a hole someone has drilled in timber? Chances are VERY high, that it will be an Gauged screw. Regardless of where the guitar was made, or when it was made. Wood screws are gauged/Imperial.

If your working with a “bolt” (bare with me, I know that there are next to no “true bolts” on a guitar, but for simplicities sake) – a screw without a point? That’s going to “thread” into something with a threaded recepticle? A nut? A humbuckers leg? A humbucker bobbin? A bridge saddle? Things become a little come complicated, because you could be working with an Imperial thread, of you could be working with a Metric thread, and the only way to know, is to measure unfortunately.

To fill you full of dread, I’ve a box of “#3 humbucker height adjustment screws” and I’ve got a box of “M3 Humbucker height adjustment screws” – ones 3mm diameter, ones 2.4mm diameter – but they both come from the same factory, and I know for a fact, both have turned up on Epiphone Les Pauls made over the decades.

There is VERY little logic in where metric or imperial threads turn up I’m afraid. There are metric threads on Gibson® guitars, and there are Imperial threads on Squier® guitars made in entirely metric countries. So, if I can give you any advice what so ever? Figure out how to measure screws (Digital callipers are cheap, and accurate enough for guitar work!)

What does UNC/UNF/Course/Fine mean?
This doesn’t really come up with wood screws (but its still true! Seemingly, no one bothers to measure it, presumably because, we’re talking wood screws, rather then machine screws/bolts, so it doesn’t really matter, because they’re cutting their own thread into the wood) but it’s very important for machine screws and bolts, because we must ensure that the threads on the male and female parts mesh perfectly.

So, Metric threads are straight again! They come in Fine thread and Coarse “pitch”, and pitch, is simply the measurement between the threads “peaks”

Now, I love the Metric system! Its easy to understand, and on the whole, it allows us to be more accurate with our measurements, but even I’ll admit, measuring the gaps between threads, is stupid. Thankfully, at least within guitars, it doesn’t come up all that often, because we’re ultimately limited by what the screw is intended for (so, an M3 humbucker pole screw, is a Coarse Pitch, where an M3 humbucker height screw, is Fine Pitch – and whilst thats stupid, you’d never use a height screw as a pole screw, or visa versa, so it sort of works out)

Imperial threads, follow a similar naming system (UNifed Coarse pitch, and Unified Fine Pitch (and there’s UNifed Extra Fine pitch too, but we never see it on guitars) and its simpler in some ways, and more complicated in others, so let’s get through this.

The pitch is measured by “the number of threads across 1 inch of length” – so, if you’ve got a screw, its got a 1” thread, and you count up all the little teeth, and there’s 40… we then measure the diameter of the thread, and figure out what gauge we’re working in – and we have the exact screw we need.

So, say we’ve got a 3.175mm diameter thread, 40 threads to the inch? We’ve got a #5-40 UNC!

Now, this has the potential to be utterly terrifying, but, thankfully, the Imperial system has a wonderful habit of being quite sensible when it has to be, so, by and large, everything is standardised! (but, again, not with wood screws – they can be measured in UNC/UNF , but they don’t follow the standards used for “bolts”) So a #4 screw will always be either a 40 UNC or a 48 UNF. So, we don’t really have to worry about it too much, thread gauge and length are more important then the thread pitch, because you’ll only ever see the correct pitch for the gauge.

And that about covers threads I think, atleast in the ideal – wood screws are much simpler then machine screws/bolts, and if you’re working with “bolts” , a set of digital callipers and an imperial thread gauge are really helpful to figure out what your need.

Guitars are weird

This, probably, isn’t entirely limited to the world of guitars, and I'm sure there are carpenters, joiners, aircraft fitters, nuclear reactor engineers and model railway enthusiasts all over the planet who’ll say exactly the same about the screws they see on a daily basis.

These measurements, and these “truths”… are all well and good in theory, but in the real world? I’ve never seen an M3 screw that was 3mm diameter thread. I’ve never seen a #4 screw that had a 5.48mm head on top of a 3.09mm thread it’s all very exacting, and, by and large, guitars don’t require screws to be this accurate.

So, if you’re measuring this stuff, and trying to figure out what screw you need? Just remember, close enough, is probably good enough, and, its all occums razar.  If you’re measuring a wood screw at 2.1mm diameter, with a 3.9mm head… sure, it doesn’t exactly match up with the agreed upon specs for a #2… but, its not a #1 or a #3 either, and the chances of it being a metric wood screw, are almost zero… so, it’s probably  #2.

Why?

Well, all the “stuff” I’ve written up above? It’s all true! Wood screws are imperial; machine screws/bolts are available in both imperial and metric. Imperial threads are measured in gauge and TPI count, metric screws are measured in diameter and thread pitch – and this is well known through all engineering and manufacturing – EXCEPT (drum roll!) screw factories.

Almost like some sort of sick joke – screw factories (at least, those making very small, very specific screws for guitars) just speak in metric. I’m sure they’re aware that Imperial exists, but it’s so foreign a concept for them (being in China, Korea, Japan etc – all metric countries) that, it just makes more sense to make everything metric.

So, as I sit here typing this, I am looking at 4 boxes of #3 screws, and heres what it says on each invoice.
2.5mm – PSH-Counter Sunk
2.6mm P90 Pan Head
M2.4 x 30mm humbucker height screw
#3-1.23” Oval Head

All the same screws! They’re all 2.4mm diameter (give or take), they’ve all got heads that are just over 4mm… they’re all #3 screws! The factories are just horrendous for rounding up/down/metrifying things that should remain imperial.

So, at source? Screws are wildly more confusing, because the factories only speak in metric (and they don’t pay much attention to thread pitch!) but, in the real world? Everythings a little simpler thankfully – you’ve just got to figure out if your working in imperial or metric, and go from there.

Threads and head are under/oversized

I've mentioned this earlier, but i'll double down here - Screws, Nuts, Bolts, Threads, heads? They're rarely the size they should be. They're normally close enough that it'll never matter, but, believe me when i say - the factories making guitar screws aren't working to the accuracy you or I would (and, they're right, and we're wrong!)

When working in metric, the name of the thread (M3/M4/M50 etc) is always larger than the actual diameter of the thread (M3s are 2.8mm diameter, M5 are 4.75mm, atleast on the male parts (on the females they’re slightly under) – the M is the nominal, it’s the idea “on paper” number.  In real world, atleast within guitars, being under on screw threads, and over on nut threads, is normal, and should be accounted for during measuring.

With Imperial measurements, its, seemingly, all very "in the ball pack". Theres alot of metric conversion going on, so seeing a "2.6mm diameter" screw (which shouldn't exist) on a stock list, isn't uncommon (and it may, infact, BE, 2.6mm!) - but, we simply have to group these things together into their logical place - it might be a 2.6mm screw, but, really? Its just #3 thats a bit thicker in the thread (but, at 0.2mm? Its so small a difference, its not worth worring about)

Either way, knowing your screw gauges, is a great jumping off point, but, if in doubt? We've got the 100% accurate dimensions under the Technical Specification tab.