For us oldies:
System 1.1/2.0, Finder 1.1
System 3.0, Finder 4.1
System 3.2, Finder 5.3
System 3.3, Finder 5.4
System 4.0/4.1, Finder 5.5
System 4.2/4.3, Finder 6.0
System 6.0/6.0.3, Finder 6.1
System 6.0.5, Finder 6.1.5
System 6.0.8, Finder 6.1.8
And maybe a few in between.
P.S. aafuss1, for the record: In around System 7, they started using MacOS 7.5, 7.6, etc., at the same time Apple introduced the "smiley face" Finder/System/MacOS logo. From then on it's been commonly referred to as MacOS 8, MacOS 9, MacOS X, etc., not System 8. Usually you wouldn't use "System" unless referring to an early version of 7 or earlier.