SNI is an abbreviation for Svensk Näringsgrensindelning and consists of branch codes used to classify companies and work places according to the activity conducted.
Here you'll find all the SNI codes: https://www.scb.se/dokumentation/klassifikationer-och-standarder/standard-for-svensk-naringsgrensindelning-sni/
A company and/or work place can have several activities and branch codes (SNI-Codes). The SNI branch codes consists of 5 digits, of which the first four must correspond to the EU standard Nace. The fifth digit in SNI is used for national divisions.