What is the name/number of this brick
This is a 3743 - Technic, Gear Rack 1 x 4 and there are 2 times 2 of these in your picture (2 on the left and 2 on the right).



I guess your description is a little vague, because if you are talking about the middle part (the shining light gray pieces), they are actually not bricks/tiles, but the axle end of an NXT motor (the right side of the motor in the below picture).