Bip39 wallet https://www.plurk.com/p/3hf2syltjx While it uses BIP32 approach you'll be able to still import BIP39 seeds into Electrum wallet. Also apart from BIp32 there is BIP44 Model which some wallet use to the era of seeds. For words that only have three letters, there's no 4th letter. By way of https://thesocialvibes.com/story6051208/bip39-format-example-a-secret-weapon-for-bip39-mnemonic-https-www-youtube-com-channel-ucupxfytj0fb78sq55hu6ocw