055 Subfield $a - Classification number:

Subfield $a contains the classification number portion of the call number. Alternate call numbers are recorded in separate 055 fields.

Examples:

055 01$aFC3099

055 02$aFC2949*

055 01$aHB31

055 00$aHB31$bS54fol.

[Multiple 055 fields; LC class number, and NLC call number.]