This 500 piecer seems to be wooden and I’m calling it a semi-grinder. Its pieces are thin but very stiff, and lock together very tightly. All the pieces are essentially alike, as shown in the above image. That’s the grinder part. The semi part is that the back of the pieces have a capital letter on them. So…if you turn over two of the pieces that “seem” to be connected, you can determine if they are by checking that the letters match at the connection sides. Also, whether the pieces are in the landscape mode or the portrait mode can be checked out by the letters on their backs.