This new fixture is small, lightweight, and designed for the workbench It quickly and easily adjusts from 15 to 60 degrees, locks securely into place by a built in handle, and provides a more rigid support than foam. This fixture that holds the book, or boards, open in a wide variety of positions to reduce strain while performing treatments. The small size permits it to be used inside a book to work on board edges and corners. It can also be used to support a textblock upright when rebacking or humidifying warped vellum boards, although additional weights may be necessary to stabilize it. I use this fixture constantly, from initial examination throughout the treatment. The natural, translucent .25 inch thick polypropylene platens are lined with an easily replaceable .0625 inch thick closed cell polyethylene foam ( aka. Volara). The adjustment mechanism is 6061 T6 aluminum and a comfort grip handle, which has a lower profile than the platens at any angle, so that relatively large books can be supported. More information here. Variable size, the platens are 6 x 8".
The last image shows an improved the adjustment mechanism. It is now much less "floppy" since it uses twin pivot points. The platens now open to 90 degrees. All Book Jacks now have this.