Manually positionable work element

Apparatus for positioning a work element on a support rail, comprising, in combination,

• at least one carriage adapted to be movably mounted on said support rail said carriage including a top member adapted to be supported on said support rail, and at least one side surface member connected to said top member and depending adjacent said support rail, so that said work element may depend therefrom;
• bearing means operably connected to said carriage and adjustable between engaging and retracted positions, said bearing means adapted to contact said support rail when in its engaging position and facilitate movement of said carriage along said rail;
• means for selectively positioning said bearing means between engaging and retracted positions, said means comprising over-center toggle mechanisms connected to said bearing means, said toggle mechanisms movable between first and second positions, so that said bearing means may be in its engaging position when said toggle mechanism is in its first position and said bearing means may be in its retracted position when said toggle mechanism is in its second position;
• and
• means for preventing the advance of said carriage along said support rail when said bearing means is in its retracted position, said means being adjustably connected to said carriage and adapted to engage said support rail.