Alco- I wonder what's the story here

That's quite common - you drill a small hole next to the mounting hole and the tab on special washer sits in the small hole preventing switch rotation.

Save drilling a D-shaped hole.

Cheers

Syd Rumpo Inscribed thus:

But the flat doesn't go all the way to the top of the threads !

Whilst your suggested arrangement might look nice in a Solidworks 3D assembly model, with no interference or other obvious problems, I'm at a bit of a loss as to how one would go from the parts as shown to the assembly in real life.

Spehro Pefhany Inscribed thus:

Without the flat continuing to the top of the threads you couldn't assemble the anti rotation washers.

D'oh.

Below the Digikey image you reference is the note:

"Image shown is a representation only. Exact specifications should be obtained from the product data sheet."

If you access the mechanical drawings and data sheet, available on the same Digikey page, you will see the actual situation.

John S

Bzzzt. Nope.

The bushing drawing is incomplete (only shows the thread and length)

The part drawing shows a slot (not visible in the photo) but no flats

The actual part wot I have on my desk looks like this:

The anti-rotation washer does not look like the one in the photo, it actually works.

Can anyone come up with a remotely plausible explanation (other than the obvious one of a face-palm screw-up) of why those partial flats are on there?

I'd go with the face-palm. Looks like a pretty obvious oopsie.

Maybe for a post-install U-thingy, with the top threads left full to make the double-nut assembly stronger.

You are supposed to beam it across the non-flattened area, using a tricorder.

:-)

That's the best I could come up with-- then I saw the Digikey photo of the washer and the penny^H^H^^H nickel dropped.

Darn, and my tricorder needs a fresh set of AA's.

Probably because it's better looking that way. Also easier to clean!

Cheers

Phil Hobbs

is there a flat on both sides or just one?

-Lasse

MTM106DPC.jpg

OK so far. Seen that before. Now how do you get the washer on?

?-)

MTM106DPC.jpg

With a clear and reliable photo i am beginning to wonder if i missed something. I think i see a way to assemble it in a real panel, but it is really going to bite if it is soldered to a PCB. Most especially if not at the edge.

??-)

Yep. The waterproof rubber boot seal thing that fits over the toggle lever doesn't seal if there's a gap in the threads. 1980's versions of AlcoSwitch and C&K switches were milled flat all the way to the top of the threads, and leaked badly. There are probably similar issues with pressurized enclosures with air leaking through the switch threads.

I think some people might be confused. You are asking why they machined part of the thread away. (And not about flat on the thicker part of the bushing that fits the D shaped washer.) (Or I'm confused.) So maybe they touch down with the mill on the threads to 'find' the depth and then mill the D in the bushing. That's my only guess.

George H.

Ahh, never mind... I'm confused.. nothing new.

George h.