LTO-5 Barcode labels specific to tape manufacturer ?

Barcode label formats are specific to the brand of the tape library that you use, not the brand of the tape.  For example, if you are using Quantum tapes in a HP library, you must get barcode labels which are suitable for HP library and not Quantum.

Yes, usually the tape drive vendor has certain specifications as to how the barcodes should be.

so for dell Powervault 124T with lto5-140 (quantum drive) do I order the dell or the quantum labels ? I cant find dell lto-5 labels... 

Check the link below as I think this relates to ordering custom barcode labels from Dell:

http://www.dell.com/learn/us/en/04/business~solutions~whitepapers~en/documents~dell-storage-lto-ultrium-barcode-config.pdf?c=us&l=en&s=bsd&cs=04&layoutvariation=modal&modaltype=box&position=center&modalwidth=600&modalheight=600&modalscroll=yes&ovrcolor=#000000&ovropac=50&modaltarget=iframe&delphi:gr=true

Check the user guide for your tape library to see if they have any specific bar code label requirements.

For the most part, LTO bar code labels are now universal.  If you purchase from a reputable source, they are highly likely to work.  Just ask for a sample or check their refund policy if they do not work.

There were a FEW libraries many years ago that were picky about their labels, but it is unlikely that you have one of those now.