This is the Assorted Black Baseplates by BricTek. Suitable for Ages 4 and Older.
Compatible with other leading brands.
Assortment includes * Two 10" x 5" (254mm x 127mm * Two 3-1/8" x 6-1/4" (79.37mm x 158.75mm * Four 2-1/2" x 2-1/2" (63.5mm x 63.5mm * Two 1-7/8" x 3-1/8" (47.62mm x 79.37mm * Four 1-7/8" x 1-7/8" (47.62mm x 47.62mm * Two 1-1/4" x 3-1/8" (31.75mm x 79.37mm * One 1-1/4" x 1-7/8" (31.75mm x 47.62mm).
This high-quality product is 100% compatible with the more expensive Lego brand, just as advertised.
Since the product description doesn't give any details on what size baseplates you are getting, this is what you can expect:
Two 16 x 32 Plates
Two 10 x 20 Plates
Four 8 x 8 Plates
Two 6 x 10 Plates
Four 6 x 6 Plates
Two 4 x 10 Plates
One 4 x 6 Plate
The plates are cleverly fitted together to take up as little room as possible in the box. When I first opened the box I was worried that I wouldn't be able to separate them, but with just a few seconds of careful fingertip prying I found that they can be pulled apart quite readily. I plan to put them back together in the same pattern when it is time to store them.