Brass threaded stack spacers. These spacers and useful for positioning components at an exact height in the stack.
Thread: M2 (2mm)
Outside Diameter: 3mm
Material: Brass
2mm – Weight: 0.006 grams each
3mm – Weight: 0.01 grams each
4mm – Weight: 0.013 grams each
5mm – Weight: 0.017 grams each
6mm – Weight: 0.021 grams each

I like to use these threaded stack spacers as “StopLocks” in the stack. Because these spacers are threaded, when used with Loctite 243 they hold their position and prevent any force from the top nut being transmitted through to the Flight Controller dampeners.

As they also have a narrower diameter, these threaded spacers can be used in tight builds where clearance is limited.

Another handy use is as shown below. The holes in this ESC are M3 which is the size hole used for M2 dampeners. If you don’t want to use dampeners on your ESC, you can use these spacers which fit neatly inside those holes.