Stratocaster® Screw-In Tremolo Arm Threading Differences

This article strictly references genuine Fender® Strat® tremolo bridges that accept a 10-32 or 5mm screw-in tremolo arm. These two screw-in threading types are what are found on Genuine Fender® Strat's® that accept a screw-in tremolo arm, no matter if they are made in American, Mexico or Japan.  The term "Genuine Fender Strat" within this article does NOT include "Squier by Fender Strat's" which may accept a 5mm or 6mm (M6 x 1.0) screw-in tremolo arm, we are strictly referring to the tremolo arms and tremolo bridges for true genuine Fender® Strat's®, NOT Squier's.  The information presented here is taking into consideration that the Strat® in question has the original tremolo bridge that was installed by Fender® when the guitar was new, no aftermarket bridges are considered here.

Based on the amount of discussions we read about "which tremolo arms fit which tremolo bridges" or "what is the tremolo arm attachment threading on a particular tremolo arm or within a particular tremolo bridge", it has become obvious that there is confusion and miss-information as to which tremolo arm threading is found in genuine Fender® Strat® tremolo bridges and tremolo arms.

All American Strat’s® since 1954 that accept a screw-in tremolo arm are threaded with UNF 10-32. or more commonly referred to as 10-32. The 10 refers to the diameter of the material (or tremolo arm) which is #10 or 3/16" and the 32 refers to the number or count of threads per one inch. 

Your typical import genuine Fender® Strat’s® (MIM & MIJ) that accept a screw-in tremolo arm are metric 5mm (M5 x 0.8).  The way a metric threading is described is a little different then an American threading. The M5 is the diameter of the material (or tremolo arm) which is 5mm and the 0.8 is the distance or measurement in millimeters between each individual thread. It can be a bit confusing since American threading pitches are determined by how many threads per one inch of threading and the metric threading pitches are determined by the measurement in millimeters from each individual thread to the next.

Often found written in various guitar discussion forums one will post that since they have installed an American 10-32 tremolo arm successfully in their MIM OR MIJ Strat® that it must mean their tremolo bridge has 10-32 threading in the tremolo block. This is not true if the MIM or MIJ Strat® still has the original tremolo bridge installed. Here is the reason why; American 10-32 threaded tremolo arms have 32 threads per inch and the 5mm (M5 x 0.8) has 31.75 threads per inch, there is only 1/4 of a thread difference in 1 inch of threads between the 10-32 and 5mm, so since the thread pitch is so close to being the same it really does not factor in with fitment issues, it is the diameter differences between the 10-32 and 5mm that forces the issue of correct fit. The diameter of the threaded portion of the 10-32 and 5mm tremolo arms are separated by approximately 0.009". 10-32 threads are typically cut or rolled onto 3/16" (0.1875") diameter rod and 5mm threads are typically cut or rolled onto 5mm (0.1968") diameter rod, this is where the 0.009" difference is referenced. Typically a genuine Fender production American Strat 10-32 tremolo arm threads will be in the 0.182" to 0.185" diameter range and the 5mm threads will be in the 0.188" to 0.195" diameter range. One can erroneously screw a 10-32 American tremolo arm into a 5mm bridge because the thread pitch is so close to being the same but the diameter of the tremolo arm is smaller so it will screw in with no apparent problems, but it is NOT a wise thing to do or a correct fit. You cannot do the opposite where you take 5mm tremolo arm and attempt to screw it into an American Strat® tremolo bridge designed to accept a 10-32 threaded tremolo arm because the threaded hole in the tremolo block is smaller in diameter for the 10-32 threads. The 5mm tremolo arm will bind while attempting to screw it in after less than 1 turn, so it would become quite obvious that it is not the correct tremolo arm. You will probably never read a post in a discussion forum where someone mistakenly states that a 5mm tremolo arm fits just fine in a bridge designed to accept a 10-32 threaded tremolo arm, it just won't work...  But you will read about the other way around all the time.

Another post we find in discussion forums is that when someone mistakenly installs a 10-32 tremolo arm in a metric 5mm tremolo bridge is that it seems to fits better than the original 5mm tremolo arm did, it is no longer floppy or loose when all the way installed.  This is because by the time the incorrect (10-32) tremolo arm is screwed in so far as to be installed enough for use, the miss-match of threads are now beginning to bind and this will take up the slack and wobble that was experienced when the correct 5mm tremolo arm was installed. Never mistake this for a correct solution, you will eventually damage the threads in your tremolo block and tremolo arm.

A quick and easy test to determine which threads you have in your TREMOLO BRIDGE would be to get a metric 5mm (M5 x 0.8) machine screw of at least 1" in length (25mm) and attempt to screw it into your bridge with finger pressure / tightness only, NEVER force it!  If it is truly 5mm then it will screw in just fine, if it is 10-32, it will not. You CANNOT perform this test by going the other way around by trying a 10-32 machine screw since it will screw into both the 5mm and 10-32 bridge and will tell you nothing.

If you still have a question as to what bridge may be in your Strat®, look up the Service Diagram for your model of Strat® and locate the part number of the bridge installed and reference the bridge part numbers below.  There may be some bridge part numbers in the service diagram that are not listed below or simply not available as replacement parts and often this occurs when a unique part number of a bridge is only referenced in a complete guitar, but its counterpart as an exact replacement is a different part number which is used for replacement part sales only.

Unfortunately Fender® is not a source of 100% accurate information for which tremolo arm threading is used in some of its tremolo bridges because they have published incorrect specs for a number of bridges, see below.  Typically you can pretty much conclude which tremolo arm threading is going to be in a tremolo bridge by where it is made, typically USA manufactured bridges will be 10-32 and offshore manufactured bridges (imports) will be 5mm.  However, this is not 100% true but a good rule of thumb and starting point for evaluation.  The 007-2290-000 American Special / Hwy 1 tremolo bridge is a good example of an exception. It is made by Ping in Taiwan but accepts an American 10-32 tremolo arm, it has #4-40 intonation screws, #4-40 saddle height screws but has metric M4 x 0.7 top plate mounting screws, so even though it is an import bridge made in Taiwan by Ping it uses mostly American screw threading throughout with the exception of the top plate mounting screws.

Also remember when installing (screwing-in) a 10-32 or 5mm tremolo arm in a Genuine Fender® Strat® tremolo bridge that it will go in at an approximate 10 degree back tilt angle leaning or tilting toward the rear or end of the body (behind the bridge), these tremolo arms do not simply screw straight down into the bridge or tremolo block. If you do not take this into consideration when installing a tremolo arm there is the possibility you may damage the threads on the tremolo arm or bridge or both, so be careful when screwing in a tremolo arm, never force it for any reason, if it begins to bind, get tight or you feel too much resistance, stop and back it out and reassess your tremolo arm insertion angle, that you have the correctly threaded tremolo arm for your particular bridge or that the threads are not already damaged on the tremolo arm before you create damage that may require repairs or replacement components. There is an exception to this 10 degree back tilt with those tremolo bridges that have the half-thickness tremolo blocks, you can confirm this by removal of the back plate on your Strat, if you have one of these bridges then your tremolo arm will not have the described 10 degree back tilt, it will go in perpendicular to the flat surface of the top plate.

Below are Fender® part numbers for bridges, tremolo blocks and tremolo arms and the correct threading used for the installation of the tremolo arms. You'll notice a number of Import Tremolo Bridges that Fender® incorrectly states they accept a 10-32 tremolo arm, but those in fact accept a 5mm tremolo arm, that sure lends to a lot of the confusion.

September 30, 2015 @ 16:02