It seems that both .sit and .1 files are or were in the past associated as Stuffit compressed archives. As such, your best option to extract/convert any of these would be to use the original software.
Convert StuffIt archive format to Stuffit archive file.
We have found 4 software records in our database eligible for .sit to .1 file format conversion.
Microsoft Windows software - convert sit to 1 on Windows
Stuffit is easy to use utility used to create and extract file archives. It is able to create ZIP and SITX archives. StuffIt also opens compressed and encoded attachments and file downloads in over 25 different formats including StuffIt, Zip, RAR and Tar.
Convert from sit file
to 1 file
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned sit to 1. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
StuffIt Deluxe is commercial compression utility, that supports about 25 archive formats such as ZIP, GZIP, SIT etc.. StuffIt has also integrated own SIF StuffIt Image Format used to compress picture images. StuffIt Deluxe is available for Microsoft Windows and Mac OS X.
Apple macOS / Mac OS X software - convert sit to 1 on OS X
StuffIt for Mac is archive utility that is able to create ZIP and SITX archives as well as extract 25 different formats including StuffIt, Zip, RAR and Tar.
StuffIt Deluxe for Mac is utility used to backup, share, archive, encrypt and shrink photos, music, and other documents. It supports variety of archive and compression file formats.