The Home Bed Style Adjustable Bed Rails can adjust to accomodate a king size bed.  Can also be used as Queen size bed rails. they fit all home style beds and rail length can be adjusted without tools .

Other Features:

"Crossbars that are easy to install and remove.
Adjusts between 36"" and 72"".
Crossbars come with extensions that will accommodate a KING SIZE BED.
Rail length can be adjusted without tools to 37"", 43"" or 57"" long.
Fits all home style beds.
Easily adjusts up or down with spring-loaded release.
Attractive brown vein finish.
Constructed of 1"" steel.
Limited Lifetime Warranty."