What is a .sit file?
A .sit file is a Stuffit archive, much like ZIP files today, except that .sit is a proprietary archive format from the 90's which allowed Mac users to confidently "stuff" their files, applications and documents into a flat file that could then be copied to a non-Mac hard drive partition, namely a DOS (FAT32) or Windows (NTFS) partition, without any risk of DATA corruption.
You see, throughout the 80's, 90's and all the way up to mid 2000's, anybody using any Mac OS version prior to Mac OS X was using .sit archives to transfer their files onto PC's, servers or to send them by email or FTP, for instance, since transfering any pre-OSX era file to a non-Mac partition or by an ASCII encoding way would destroy the file's resource fork, which would essentially render the destination file totally useless. Effectively, except very early 1984 Macintoshes, they all used HFS or HFS+ partitions to store their files (and their resource forks) all the way up to Mac OS X 10.13 High Sierra which shifted away from HFS+ in favor of APFS.
Some document formats did not use a resource fork even back then, such as plain ASCII text documents, archives (.hqx, .bin, .zip, .cpt, etc... which all of these and many more can be expanded using Stuffit Expander) and .sit archives of course :P But just about anything else in a pre-2003-ish Mac, especially applications, all had a highly sensitive resource fork.
How to use or extract .sit archives contents?
To extract or expand a .sit archive, you simply open it with Stuffit Expander UNDER MAC OS of course, even if Stuffit Expander had a version for Windows at some point, since it makes absolutely no sense to expand an old Mac file stuffed in a .sit archive outside of a HFS partition. If you have time to lose, then do it and see your expanded files destroyed, stripped of their resource fork, rendered totally useless.
Always try to use the most recent version of Stuffit Expander available for your Mac OS since there were some changes in the Stuffit format throughout the years. Everything on MR should be expandable using Stuffit Expander 5.5.
Under Classic Mac OS (before Mac OS X)
Mac OS 7.5 to Mac OS 9.2.2: Stuffit Expander 5.5
Mac OS 6.0 to Mac OS 7.1: Stuffit Expander 4.0.2
Under Mac OS X
Use The Unarchiver
Do not attempt to expand any .sit file under Windows.
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