The book stop has three brass ‘pins’ screwed into its bottom face which engage a row of three brass sockets that I sunk into the reading slope close to the hinged edge. It fits snugly, requiring a reassuring degree of coaxing to remove.
Coincidently, I see Christies are auctioning a similar “George II Mahogany adjusting reading table” with an identical book stop arrangement in their Decorative Arts Europe sale (sale 2350) on 21 – 22 October 2010 at Rockefeller Plaza, New York. The pre-sale estimate is USD$5,000 – $8,000.
The mahogany table up for auction has two additional rows of sockets, allowing for further adjustability.