Why is this query giving an error? The error is: SQL Error (1062): Duplicate entry '0' for key 'PRIMARY'

```
INSERT INTO `static_number_source` (`IDString`, `source`) VALUES
('RUS-001A', 'Thub'), #one
('RUS-001A', 'Fort'), #two
('RUS-002A', 'Thub'), #three
('RUS-002A', 'Fort'), #four
('RUS-003A', 'Thub'), #five
('RUS-003A', 'Fort'), #six
('RUS-004A', 'Thub'), #seven
('RUS-004A', 'Fort'); #eight

```