An endless elongate structure adapted to circulate around a path. The endless elongate structure comprises a central longitudinal portion and two lateral longitudinal portions on opposed sides of the central longitudinal portion for supporting the central longitudinal portion therebetween. The central longitudinal portion and two lateral longitudinal portions are connected together by joiners. The central longitudinal portion is adapted to be assembled into a movable tubular formation which is adapted to be continuously assembled at one end thereof and continuously disassembled at another end thereof during movement of the elongate structure along the path. The central longitudinal portion has two longitudinal edge sections adapted to be releasably connected together for assembling the tubular formation by a slidably interlocking connector. The slidably interlocking connector is integrated with the two longitudinal edge sections by joiners.

An endless elongate structure adapted to circulate around a path. The endless elongate structure comprises a central longitudinal portion and two lateral longitudinal portions on opposed sides of the central longitudinal portion for supporting the central longitudinal portion therebetween. The central longitudinal portion and two lateral longitudinal portions are connected together by joiners. The central longitudinal portion is adapted to be assembled into a movable tubular formation which is adapted to be continuously assembled at one end thereof and continuously disassembled at another end thereof during movement of the elongate structure along the path. The central longitudinal portion has two longitudinal edge sections adapted to be releasably connected together for assembling the tubular formation by a slidably interlocking connector. The slidably interlocking connector is integrated with the two longitudinal edge sections by joiners.

An endless elongate structure adapted to circulate around a path. The endless elongate structure comprises a central longitudinal portion and two lateral longitudinal portions on opposed sides of the central longitudinal portion for supporting the central longitudinal portion therebetween. The central longitudinal portion and two lateral longitudinal portions are connected together by joiners. The central longitudinal portion is adapted to be assembled into a movable tubular formation which is adapted to be continuously assembled at one end thereof and continuously disassembled at another end thereof during movement of the elongate structure along the path. The central longitudinal portion has two longitudinal edge sections adapted to be releasably connected together for assembling the tubular formation by a slidably interlocking connector. The slidably interlocking connector is integrated with the two longitudinal edge sections by joiners.

An endless elongate structure adapted to circulate around a path. The endless elongate structure comprises a central longitudinal portion and two lateral longitudinal portions on opposed sides of the central longitudinal portion for supporting the central longitudinal portion therebetween. The central longitudinal portion and two lateral longitudinal portions are connected together by joiners. The central longitudinal portion is adapted to be assembled into a movable tubular formation which is adapted to be continuously assembled at one end thereof and continuously disassembled at another end thereof during movement of the elongate structure along the path. The central longitudinal portion has two longitudinal edge sections adapted to be releasably connected together for assembling the tubular formation by a slidably interlocking connector. The slidably interlocking connector is integrated with the two longitudinal edge sections by joiners.

A ball retainer includes a chain belt, a hook, and a slot portion. The hook is arranged on the first end of the chain belt. The hook includes a neck portion, a hook body, two leaning protrusions, and a limiting protrusion. The hook body is connected to the neck portion. The two leaning protrusions extend outward along the short side direction of the chain belt toward two sides of the hook body, respectively. The slot portion is arranged on the second end of the chain belt. The slot portion includes a slot, two abutting portions, a connecting portion, and a receiving portion. After the hook is correspondingly engaged with the slot portion, the hook body is accommodated in the slot, the two leaning protrusions correspondingly lean against the two abutting portions, the neck portion leans against the connecting portion, and the limiting protrusion is correspondingly accommodated in the receiving portion.