i have an old seiko H601-8020 and i bought the tools, vise and wrench, to change the battery. i tried the vise and wrench out on a same year and model seiko i have that the battery was left in way to long and it is ruined, sent it to two match makers and they said it wasnt worth it to fix, anyway i found the same exact one, working. so i was able to get the back off the bad one easy enough but the oring was so badly elongated that there was no way it was going to go back in. im sure if i would of spent a long time i could of gotten it but the watch is shot anyways. so i figured it would be a good idea to have a new oring so when i finally have to replace the battery in my good one ill be able to use it. i found assortments on ebay but how do i find out which one i need ?