Bolt attribute

I guess you are using the NEW bolting method, aren't you?
Navigate to your valve SCOM.
As Pitch was saying, youn need to set its BLRFARRAY attribute in order to point to two different BTSE.
I.e. BLRFARRAY /AAVGBB2-8-20 /AAVGBB2-4-20

Then in your spec you just need one entry for 20mm diameter bolt:

HEADING
TYPE   NAME         BDIA   BTYP   CATREF     DETAIL       MATXT        CMPREF   BLTREF
DEFAULTS
-      -            -      STUD
BOLT   */20mmSTUD   20.0   STUD   /STUD   /STUD-D   /STUD-M   =0       /ABGAB

I guess you are using the NEW bolting method, aren't you?
Navigate to your valve SCOM.
As Pitch was saying, youn need to set its BLRFARRAY attribute in order to point to two different BTSE.
I.e. BLRFARRAY /AAVGBB2-8-20 /AAVGBB2-4-20

Then in your spec you just need one entry for 20mm diameter bolt:

HEADING
TYPE   NAME         BDIA   BTYP   CATREF     DETAIL       MATXT        CMPREF   BLTREF
DEFAULTS
-      -            -      STUD
BOLT   */20mmSTUD   20.0   STUD   /STUD   /STUD-D   /STUD-M   =0       /ABGAB