This part is correct for most XK140 and all XK150 cars.
21 inches front to back, hinges screwed to edge. 3/8" birch plywood, 8 ply, shaped and drilled.
Original factory part number BD14129 (wood only). This is correct for cars in which the wooden spare wheel cover was covered by an aluminum skin.
A few XK140 cars had a cover that wasn't covered by an aluminum skin and measured 21 3/8" front to back, and had hinges that screwed through the top surface; see Related Products for XW8+ below.