Slide rail assembly and slide rail thereof

A slide rail assembly, comprising:

• a first rail comprising a first wall, a second wall and a first middle wall connected between the first wall and the second wall, a passage being defined by the first wall, the second wall and the first middle wall;
• a slide assisting device arranged in the passage of the first rail, and the slide assisting device comprising a first rolling member;
• and
• a second rail movable relative to the first rail, the second rail comprising a first side wall, a second side wall and a second middle wall connected between the first side wall and the second side wall;
• wherein the first middle wall of the first rail is formed with a first ball groove, the second rail further comprises a first extension wall, the first extension wall comprises a first extension section, a second extension section and a first middle section connected between the first extension section and the second extension section, the first extension section is extended from the first side wall of the second rail, the second extension section is extended toward the second middle wall of the second rail, and the first middle section is formed with a second ball groove;
• wherein the first rolling member is located between the first ball groove and the second ball groove;
• wherein the second wall of the first rail comprises a third supporting section and a fourth supporting section bent relative to the third supporting section, and the fourth supporting section is configured to hold the second side wall of the second rail;
• wherein the slide assisting device further comprises a second rolling member;
• wherein the first middle wall of the first rail is further formed with a third ball groove, the second rail further comprises a second extension wall, the second extension wall comprises a third extension section, a fourth extension section and a second middle section connected between the third extension section and the fourth extension section, the third extension section is extended from the second side wall of the second rail, the fourth extension section is extended toward the second middle wall of the second rail, and the second middle section is formed with a fourth ball groove;
• wherein the second rolling member is located between the third ball groove and the fourth ball groove.