Internal vs. External Star Lock Washers

[David Paule]

Which should I use where?

While my immediate application is for steel screws into threaded aluminum, I'd appreciate learning about the reasons for one or the other generally.

Thanks!
Dave
RV-3B, still, yes, even now, skinning the fuselage

[mturnerb]

My WAG is that it has to do with size of the bolt/screw head - needs to cover teeth of washer. Just a guess though

[ColoCardinal]

My understanding agrees with Mturerb. Fasteners with a larger head, in proportion to the thread diameter, do best with external tooth washers. Those with smaller headed fasteners (such as filister heads) do better with internal tooth washers. The electronics industry often uses washers with teeth on both internal and external of the same washer.

[JonJay]

This seems to agree with above thoughts:
https://www.seastrom-mfg.com/washers_lock.aspx

Great question.