Hi Finn, you are spot on with the thread diameter being 7/16 inch. Suggest trying a UNC or BSW nut of that size. They are virtually the same coarse thread with pitch of 14 threads per inch.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone