440 Subfield $v - Volume number/sequential designation:

Subfield $v contains the volume number or other sequential designation that identifies the particular item in a series.

Examples:

440  #0  $aEnvironmental science research ;$vv. 4

440  #0  $aRussian titles for the specialist,$x0305-3741 ;$vno. 78

440  #0  $aRomanica Gothoburgensia,$x0080-3863 ;$v12, 16