The mystery uncovered
“Tremolo” arms or “Whammy” bars as they’re sometimes called, are used with a “Tremolo” (the correct term is actually Vibrato) but that is another argument all together. The arm is used to actuate the tremolo device in order to raise/ lower the pitch of the strings. The arm design is simple; generally arms have 2 bends in them but can have more if needed for a purpose.
Starting at the butt end, the first bend is about ½” to ¾” above the tremolo and is the bend that angles the arm down toward the headstock. The bend is almost a 90 degree angle. You will need more dive room for the arm tip, so the angle is less than 90 and can be as low as 75 degrees depending on the spring pull below. It’s all in the design of the tremolo system and its requirements. The second bend usually comes about two thirds way down the arm and is generally about 8 degrees inward depending on design. The arm is bent inward toward the center of the guitar depending if the arm is for right handed or left. The unbent rod can be anywhere between 7.5 inches and 8.5 overall for guitar tremolos and up to 12” for bass tremolos. The butt end can be either square or rounded, threaded or grooved. The arm diameter can be 5mm, 5.5mm, 6mm or 3/16”, 7/32” or .250”.
Assuming you have no clue what type of arm you need, here are the questions you need to answer:
Is your tremolo Metric or an Imperial (USA) product?
Chances are it’s imported to the USA and in a metric format. All items produced off shore of the USA are considered metric. All Floyd Rose tremolos whether licensed or not, are metric except the four Kahler fulcrum versions. Basically it seems, most tremolos were, and still are, made overseas in Asia or Mexico. However every Kahler system on the planet and a handful of USA made Charvels (the brass models) USA made Fenders and about half of the PRS tremolos are made with USA specs as well as Gibson Bigsbys.
Is the arm hole threaded?
Hint: you can take off the back spring plate if necessary to see the bottom side of the lower block and the back side of the arm hole. You should be able to see some threads up inside the arm hole from underneath. If you do not, you will probably see a BB or some type of detent spring wire near the end of the hole. Look for a spring wire clip or a BB and retainer ring attached to the out side of the holes shaft near the lower end. This item would be pressed into the arm channel to snap into the groove of the passing arm.
What is the arm diameter needed?
First a little understanding about metric/ inch diameter sizing… the way metric (mm) sizing is described is somewhat different than how USA sizing is described. Surely if you know anything about wire gages or screw sizes, you will understand the similarity here. The smaller the number, the thinner the item and visa versa. But metric and inch have different scales… so to speak. For example, the metric way of describing a size and thread pitch is like this: M5-0.8. The big “M” stands for metric followed by the size number, in this case 5 followed by a dash and the pitch.
An Imperial (USA) size and thread pitch looks like this: 10-32. The “10” is the USA arm size followed by a dash, and the pitch. You will need to use calipers to measure the arm or the arm hole. Measure in mm if it’s a metric tremolo or in inches if it’s USA made. You can go to any machine shop or Fastenal store for the measurement. Your arm diameter choices are generally 5mm, 5.5mm or 6mm for metric and 3/16” or 1/4” for USA.
Understanding thread pitch...
The second number is thread pitch. Metric pitch and USA pitch is determined in different ways. The metric system is a base 10 system. 0.8 or 1.0 for example is how metric pitch is written. The individual windings are exactly .08mm apart or 1.0mm apart respectively. So in the M5-0.8 example, the size is 5, and the distance between threads is just .08 mm.
USA pitches written similar but are determined by how many threads are within 1 inch. In the example above, the size was 10-32 which simply means size 10, - 32 threads per inch. Or you can have 40 per inch. See the picture to the right using a 6-32 and 6-40 knob with a 1/4" shaft length ->
BEWARE! You should never, for any reason, substitute an arm that is the incorrect size but “seems to fit well”, here is the reason why…
using a similar sized and commonly used M5-0.8 arm in place of a 10-32 arm for example, remembering the 10-32 threaded tremolo arms have 32 threads per inch while the M5 x 0.8 arm (which is the same as the USA 10), has 31.75 threads per inch. That means there is .25 less linear thread in that same USA threaded inch between the 10-32 versus the 5mm, so since the thread pitch is so close to being the same you really don’t notice after its screwed in all the way. And that is a bad thing… why? Because by the time the incorrect M5-0.8 tremolo arm is screwed in all the way, the miss-match of pitch is now starting to close in and bind up taking up the slack and wiggle in the arm hole. Never mistake the consequences, you will eventually damage the threads in your tremolo block and tremolo arm when you start to dive-bomb or pull up. Just do the right thing, get it measured. You can go to any machine shop or Fastenal store for the measurement. Your arm diameter choices are 0.8 or 1.0 for metric pitch, and 28 or 32 for USA pitch.
What shape is the butt?
#016, 5362 Standard Arm 10-32
#018, 8537 Bass Arm .250-28
#019, 5362 Flyer Arm 10-32
#019, 8538 XL Bass Arm .250-28
#115, 8530 Fulcrum Arm .250-28
#8338, Kahler Auto Latch Arm .250-28
5362 Charvel Arm - Brass 10-32