[Koha] regarding marc tag and importing records

[vijay kumar]

Dear Member,
I have confusion regarding selecting marc tag for item type...
1) In koha...if i want to tag with marc for an item , there are two
marc tag for item type  like 942$c and 952$y
so which tag is better for representing a book items.

2) In koha mapping , tag 952$y representing itype , in this tag   is
y  in capital letter or small letter bcz when i am trying to give
952$y ie, small letter y showing  error for script.

3) If I have more than 2 subject added entry and when i assign value
650$a to each.....after importing only one subject added entry is
imported.....so what is the problem?

Thanks in advance for suggestion,

With regards,
vijay kumar
NCSI, IISc
Bangalore