Sewing supports that are placed on the outside of a case-type cover, which is therefore also sewn through as the book is sewn. Both sewing supports and pierced sewing supports can be found in this position. On printed books this appears to be a northern European phenomenon, particularly France and the Low Countries, and the case is most often made from a relatively thick parchment (usually calf) without turn-ins, but sometimes with a fore-edge envelope flap.
external sewing supports
Broader partitive concept: