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 retainer configured to mount the first rolling member;
• and
• a second rail movable relative to the first rail, the second rail comprising a third wall, a fourth wall and a second middle wall connected between the third wall and the fourth wall;
• wherein the first middle wall of the first rail is arranged with a first predetermined part bent relative to the first middle wall, the first predetermined part 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 third wall of the second rail along a height direction of the slide rail assembly toward the first middle wall to be connected to the first middle section, the second extension section is extended from the first middle section along the height direction to be away from the first middle wall, 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 first wall of the first rail comprises a first predetermined section extended from the first middle wall along the height direction, a second predetermined section extended from the first predetermined section along a width direction of the slide rail assembly, a first supporting section extended from the second predetermined section along the height direction to be away from the first middle wall, and a second supporting section bent relative to the first supporting section to be extended from the first supporting section along the width direction, wherein the second extension section of the second rail is extended toward the second supporting section from the first middle section and configured to be held by the second supporting section;
• wherein the height direction is perpendicular to the width direction;
• wherein the first middle wall of the first rail has a first surface and a second surface opposite to each other;
• the first predetermined part is substantially in an arc shape and comprises a first shoulder section, a second shoulder section and a valley section located between the first shoulder section and the second shoulder section of the first predetermined part, and the first shoulder section and the second shoulder section of the first predetermined part are protruded relative to the first surface of the first middle wall;
• wherein a predetermined extension portion of the first middle wall is extended from the first shoulder section along the width direction to be connected to the first predetermined section;
• wherein the predetermined extension portion, the first predetermined section and the second predetermined section define an accommodation space configured to accommodate a lateral part of the retainer.