PHP Code:
INSERT INTO `product` (`stock_num`, `series`, `name`, `thread_id`, `dim_h`, `dim_w`, `dim_l`, `weight`, `case`) VALUES ('10999a', 's12', 'test tein', '325', '123.6', '123', '423', '123.67', '4')
Try this, maybe the word weight or case are reserved words for MYSQL. The `something`tells MYSQL to read this as an element of the table not a function.
Tell me if it works

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