1. A server chassis, comprising:a tray, the tray including a bottom plate, two opposite side walls extending from an edge of the bottom plate, a sliding latch being protrudingly disposed at an outer side of each of the side walls;
two inner rails, each of the two inner rails being disposed at the outer side of the corresponding one of the two side walls, each of the inner rails including a through slot corresponding to the sliding latch, the through slot extending longitudinally along the inner rail, the sliding latch being inserted in the through slot to be movable along the through slot; and
two outer rails, the two outer rails receiving the two inner rails respectively, each of the inner rails being movable outwardly from one end of the corresponding outer rail,
wherein a block flexible arm is disposed on the outer side of at least one of the side walls.