Nothing special just an Allen wrench. I don't remember what size but it's a common one. You just take the screws out of either side like you're removing the link and when the screws clear the link, the washer can slide out. Just slide in the new one and push the screw through and tighten it up. I double checked all my screws about an hour after I changed them and again later that night.I gotta ask, how easy is it to swap the washers from the watch? Is a special tool required?