This 66-cell plug tray from Grodan is made for stonewool A-Ok Starter Plugs or Macroplugs. 

It's designed with shorter cells so the plugs rise slightly above the tray for easy removal when it's time to transplant your plant clone or seedling. Helps decrease the risk of root damage.

The Grodan plug tray has a wide rim that lets you hang it on top of any standard 10" x 20" nursery flat, leaving a 1/2" space below the tray. This keeps moisture around the base of the plant plugs, yet prevents root rot from being immersed in the water.

In essence, creating an inexpensive, yet effective mini-cloning system!

Will also accomodate Rapid Rooter plugs or Jiffy 7 pellets.

Grodan's easy seed and plant cloning suggestions.