My Life With Knurled Brass Nuts

A.K.A Hex Nut Versus Friction Nut

When building sub-250 gram FPV drones the parts get pretty damn small.  Hell, my 4k camera and analog video feed generator is a single 25mm board.  The flight controller, ESC's, and even an OSD are similar in size on one board.

sometimes you need small

That's some tiny shit.

Here in enters the real problem.  Fastening. The density of the PCB along with a certain level of engineering tone deafness (poor management of product line) can create real world collisions. 

Most of the time the standard parts work. M3 and M2 hardware to the rescue.  Sometimes M2 nylon hex standoffs and nuts can be too big. So big that assembly now becomes an exercise of self-immolation. 

Take a look.

Overhead use of hex nut

The above image is a hex stand off, the same X/Y dimension as a nut, clearly hitting the 65K5 (resistor?).  In fact the component has a chipped corner from  previous spinning nylon nuts.

Damaged component

The above image underscores the damage and how it was created.

Damage zoomed in.

Above image zooms in on the damage.

Another board is already destroyed after the nylon nut ripped off that exact component.  Despite a re-solder and no damage, other than jumping off the surface mount, it did not come back to life.  

Gimme Solution!

Knurled nut to the rescue.

Enter the brass knurled nut (above).  These are manufactured to be an insert or moulded component in plastic.  They are extremely handy in this scenario because of the reduced cross section (outer diameter). 

Zoom in of the knurled brass nut

The above image shows how approximately 1mm is shed from the diameter.  No corners (because of hex shape), these are round.

Overhead on the knurled brass nut

The above image shows the use of the knurled brass nut from overhead.  On a tight, dense, and poorly designed PCB these little guys save components! 

Pros, Cons, and What You NEED to know

  • Nuts are self locking (stable) only when used on a nylon screw.
  • If these are used with metal screws (threads) thread lock is required.
  • Slightly heavier than a nylon nut. A consideration to ponder but usually the weight gain is <5% of the variation on battery weight.
  • These assemble and remote with bare fingers.  Needle nose pliers can carefully extract these nuts. Carefully!
  • After about 10-30 assembly cycles your fingers will be a little raw. Plan ahead.

Buy this part now M2 Knurled Brass Nut.