internal vs. external tooth lock washers 1

[drawingboard]

Any science behind the decision to use an internal vs and external tooth lock washer? I try to use external since you make the most out of the diameter. I only use internal tooth for cosmetic appearances.

 

[nigelt]

Nobody has ever answered that satisfactorily for me either!
I have to say I came to same conclusion as yourself.
Cheers!

 

[PUTTER]

The internal tooth lockwasher is for use under screw heads since the intent of the teeth is to grip the thread on the screw or bolt. The external tooth lockwasher is for use under a nut since the teeth cannot grip the treads on the nut, they are intended to grip the surface of the nut to keep it from loosening.

 

[peglor]

Interesting idea, but any internally toothed washer I've seen doesn't touch the thread of the screw it's on.

It is true though that the bottom surface of a nut generally bulges slightly, so it's contact patch is circular or annular and slightly further from the threads the nut is put onto than an equivalent bolt's contact patch would be. The pressure distribution under the head of a bolt compared to under a nut is probably slightly different too.

Specifying the washer so the teeth line up with this contact patch could lead to externally toothed washers being used under nuts and internally toothed washers used under bolts. Never really thought about it before though.