Multi-rail concealed slide rail structure

A multi-rail concealed slide rail structure, comprising:

• an outer rail, being an elongated structure having an L-shaped cross section, one side of the outer rail being mounted to a retaining surface, another side of the outer rail being bent inward to form a first track;
• a first ball retainer, including a first holder which is formed in a G-like shape corresponding to the first track, a plurality of first rollers being provided on each surface of the first holder, the first ball retainer being fitted on the first track, the first rollers of a top surface, a bottom surface and the two side surfaces of the first ball retainer lean against four surfaces of the first track;
• a middle rail, being an elongated structure having a reverse U-shaped cross section corresponding to the first ball retainer, two side edges of the middle rail being bent in the same direction to form second tracks respectively, the middle rail being fitted on the first ball retainer, the first rollers on the bottom surface of the first ball retainer leaning against one of the second tracks, a central portion and two side surfaces of the middle rail leaning against the first rollers on the top surface and the two side surfaces of the first ball retainer respectively, a limit plate being provided at one side of one of the second tracks, the limit plate being spaced from the second track;
• a pair of second ball retainers, the pair of second ball retainers each including a second holder which is formed in a reverse U-like shape corresponding to the middle rail, the pair of second ball retainers being located corresponding to a front section and a rear section of the middle rail respectively, the pair of second rollers of the second holder leaning against two side surfaces and a top surface of the middle rail respectively;
• and
• an inner rail,
• characterized in that the inner rail is an elongated structure having a reverse U-shaped cross section corresponding to the pair of second ball retainers, two side edges of the inner rail are bent inward to form third tracks corresponding to the second tracks respectively, the pair of second ball retainers comprises a pair of second rollers and a set of second balls, wherein the set of second balls is provided on a surface of one end of the second holder, the inner rail is provided with a reversed bent portion corresponding to the pair of second ball retainers, the inner rail is fitted on the pair of second ball retainers, a top surface and two side surfaces of the inner rail lean against the pair of second rollers on a top surface and two side surfaces of the pair of second ball retainers respectively, the set of second balls at respective bottom surfaces of the pair of second ball retainers are sandwiched between the second tracks and the third tracks, the limit plate being configured to prevent the inner rail from tilting upward.