Bip39 eth https://hectorswwo172.bearsfanteamshop.com/picking-the-right-tools-for-your-bip39-generation-demands Even though it uses BIP32 technique it is possible to still import BIP39 seeds into Electrum wallet. Also apart from BIp32 There's BIP44 version which some wallet use for the generation of seeds. For words that only have 3 letters, there isn't any 4th letter. For instance https://socialbookmarkgs.com/story20080013/bip39-binary-new-step-by-step-map-for-bip39-word-list-txt-https-t-me-bip39-chat