Powermatic #3840002.  The is the locking washer for the 1/2" shaper spindle on the Powermatic 25, 26, 27, 27S shapers.  Without the tab on the washer the nut could work loose and then stand back!!!  This may fit other makes also.  The tab is under 1/16" wide and 1/16" long.  These do wear out in time and have to be replaced.    Shipping on this item is free via USPS or UPS. I do combine shipping wherever possible. I do ship internationally. Just email me and I will quote shipping to your country.