Just making this thread to help anyone who has lost this part.  I had a hard time finding the exact one.

The size of this washer is:

.53" ID
.76" OD
.015" Thickness.
overall thickness is .09"

It's just a basic 1/2" spring steel wave washer.
You can probably find it at your local nut/bolt store.

If not, you can order them from places like these:
http://www.grainger.com/Grainger/Wave-Washer-6ZA22?Pid=search
http://www.amazon.com/Wave-Washer-50/dp/B00867V2L0

Here too

http://www.mcmaster.com/#cadinlnord/9714k35/=p9lnnz

This is NOT it.

If you look at the measurements, you can easily see that this part is nowhere close to the specs of the factory ruger part for which I provided measurements in the above post.

Do NOT panic!    

McMaster--Carr has a wave washer that has worked fine for me.  It's stainless, measures a little smaller on the OD than the Ruger washer at .734, ID is within .001 at .531, thickness is thinner at .009".  They are sold in a 25 pack for $12.50 plus shipping.  

I actually like the smaller OD better as some of my barrels that I've had threaded are smaller in OD than the Ruger factory barrels.

McMaster-Carr # is:   9714K35  (as posted above).  

OK, thanks for that tip! I just ordered a bag as they look to be identical on our MKIII and our LITE.    Now my question is this - Anybody know where to get replacement thread protectors?  The MKIII is steel and thicker than the LITE one, which I think is aluminum, and I would like to buy a couple of each in case one was to be fumbled into the tall grass or something.    Anybody know a source?

Thanks,

Phil

Just call Ruger, I lost my washer and they shipped me a free replacement.
Thread protected even if they charge a small fee will at least match the rest of the gun.

OP: that amazon link is a bad link in the first post.  Can you please list the item again?  i tried a search on amazon but couldn't seem to find the right size washer.  


secondly,  do you guys use this washer when mounting up your cans?  i just got my 22/45 threaded and tried shooting it this past week with and without the washer with my Gemtech can.  They both shot fine however i liked the fact that i didn't have to worry about the can coming loose after a mag or two when i used the washer.  :)

Thoughts?