File Extension SLS4 File Format Excel 4 SLS4 stands for Excel 4. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Advanced Page Numbering in Word and Excel What exactly is Excel? How to fix this error in SQL and Excel?