11. We call a four-digit number a "Mid-ring number" if it has the following characteristics: (1) all four digits are different; (2) the thousand's digit is neither the largest nor the smallest of these four digits; (3) the unit's digit is not the smallest of these four digits. There are $\qquad$ such "Mid-ring numbers".
【Analysis】From 0 to 9, selecting 4 different digits has $C_{10}^{4}=210$ ways. Suppose the four digits taken out are $a<b<c<d$. According to the problem, $a$ can only be placed in the hundred's or ten's position, giving 2 choices. $d$ cannot be placed in the thousand's position, leaving 2 positions to choose from. The remaining $b, c$ have no restrictions, and can be placed in 2 and 1 positions respectively. In summary, there are $210 \times 2 \times 2 \times 2 \times 1=1680$ such numbers.