I have 8 Border Collies, so I can identify. Hope he doesn't get perforated bowel if he swallowed it.
The tip is one fraction (1/16"?) longer than half inch; shaft is 3 1/8"; top is 7/16"; total length is 4 1/16" or 4 1/8" on the slanted side. Both plastic ends unscrew from the shaft, but cannot be used as reset buttons on either end. Seems like it would be easier to call Sony for a replacement and then copy it, or maybe someone on this site could sell you one from their broken reader.