[1] Super Fine - Fingering Weight

What makes a yarn a #1 Super Fine?  Yarn size standards are just a rule of thumb or general guide.  Yarns that fall into this category are commonly called sock weight or fingering.  This is a rather thin yarn that for socks, is knit or crocheted very tightly.  Tightly so that they wear longer. Socks are worked on 2.25 - 3.25mm, which is a US1 - 3 needle.  Same for crochet hooks B, C or D.

Gauge can be 27-32 sts in 4 inches.  Except for shawls.  Shawls are often done on large needles for drape.  Shawl gauge will depend on the needle or hook used, and the stitch.

Yarns of this size, that come in 100-gram hanks usually have yardage of between 390 to as much as 500yds.  The most common is around 440 yds.

This yarn machine knits wonderfully on a standard gauge knitting machine near 7, 8 or 9 tension. Silver Reed SK280 and SK840.

But over the last few years, companies and hand dyers have taken this yarn to another level.   Blends are no longer just wool and nylon, but are now incorporate silk, llama, cashmere, mohair and so on. These are super silky blends.  And the colors are over the moon!  Wild and zany, to tonal shades (kettle dyed) to solid shades of the deepest hues.   These yarns are most popular in shawls.  And the more complex the better! 
When using this yarn in shawls, the needle is often a larger size to get an incredible amount of silky drape.