A recess was carved into the back board deep enough so that the strap and the decorative brass cover plate could be inset in to lie flush with the board surface. (see detail bottom left)

To prevent board breakage, I drilled a small pilot hole, slightly smaller than the diameter of the escutcheon pin which I used to attach the brass cover plate and the strap to the board. Drilling a pilot hole is especially advisable if you are using a hardwood board in order to avoid splitting the wood. It also functions as a guide to help to hammer the the pin in straight.

Details

This book in wooden boards covered in suede is used here in order to illustrat ea Romanesque style closure.

In a historically accurate model, the strap would not be attached to the rear board of the book with a brass cover plate. More likely, the strap would have been set into a recess in the board itself underneath the covering material; and it would extend out from under the covering through a slit at the foredge. There probably would have been two clasps which may have fastened onto the back board, rather than onto the front.

This hinged brass clasp design was derived from an illustration of a bronze Romanesque design in the book Archaeology of Medieval Bookbinding, 1999, by J.A. Szrmai. The illustration showed one rivet used to attach the clasp to the strap, so that is how I made the model. However, only one rivet is not advisable because the clasp would eventually tend to rotate on the strap, rather than remain in a fixed position, creating stress which would ultimately cause a tear in the leather strap.