Nunn Design ~ Patera glass domes, 2 sizes in stock 20 & 13mm. The 20mm works in the large circle bezels and can also be used in other bezels for a different affect. 
20mm sold per piece ~ 13mm sold per pair
Measurements ~ (20mm) 19.8 x 7mm depth, (13mm) 12.5mm dia x 3.2mm depth. Due to the nature of the manufacturing process of this item the sizes may vary from batch to batch. This glass dome does not fit the bezel perfectly. It is slightly smaller than the bezel.