Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_14 ( licence_number VARCHAR, maximum_diameter VARCHAR )

### Question ###
What is the license number where the maximum diameter is 400 mm?

### Accurate SQL ###

SELECT licence_number FROM table_name_14 WHERE maximum_diameter = "400 mm"