[maximalmobi7]

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The ASIN (Amazon Standard Identification Number) for the book is the 10-character string that begins with a "B".
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In calibre select your book, choose "Edit Metadata", and in the "Ids:" field add "amazon:B005MZN2B2" (without the quotes and using the ASIN you discovered). If there is something already in the "Ids:" field then separate the new information with a comma.

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Information above from other users source post, included here since I wanted to comment on that.

when you download the metadata information from amazon source under calibre, the amazon source number that was included with control-d command feature under calibre doesn't not start with an B in the string it pulls up for the ebook, I may have to manually find the correct information from amazon page for the ebook since again the download feature under calibre doesn't not have asin numbers that start with B in them. I just wanted to point this out if may be why the output kfx format is not including the thumbnail when automatic downloading the metadata from amazon under calibre with that download metadata and covers option under calibre. again the asin automatic download of metadata included of amazon: number under ids: is only numbers and no B text before the number from amazon source from calibre feature for metadata automatic download from calibre.

I think It the ids: amazon source it download the amazon 10 numbers without the B before the number that's not included in the ids: tag for the ebook. again the ebooks string doesn't start with an B in it.
I don't no if its an simple matter of putting a B before the 10 number if that not included in the source ebook.

so I deleted the ids : isbn: number , , mobi-asin: number
I have yet to reconvert the rb book to kindle book, I edit that if that works or if putting an B in the ids tag works either I don't no yet since I have yet to try it in the calibre program, still I hope at some point I can use kindleunpack since again the kfx format output size is too big from the source, its still better to use azw3 format if the source size matter to you too since kindleunpack is not useable yet for kfx format.

I don't no if the above ids: tags interfere with the thumbnails feature for kfx ebook or not, I tried putting amazon: first, then isbn and mobi-asin, but after reopening the metadata page in always put the amazon tag in the middle between the isbn 10 number and mobi-asin 10 number the ids: tag box under calibre.

amazon: keep this one, again it doesn't start with an B under the amazon page, don't no if needed to put an B before the number since it doesn't have that on the link amazon page brings up. also it is the 10 number only that metadata and covers downloads from the amazon source.



so I tried putting an string B before the number and it breaks the link to the ebook on amazon.com website, if you put in the B since the ebook doesn't have that only the number, when its just the number it does bring up the correct page, but with the b string inserted before the number it breaks the online link. I don't no if that matters for the kfx format or not.

I tried the ids: "amazon:number" only in ids: under calibre and no luck still no thumbnail image on kindle paperwrite 2, when coverting rb book into kfx ebook,

their was no thumbnail created since it doesn't load an image for the ebook at all, and the amazon link works in calibre.