When casing and screen are installed in an open hole to be gravel packed, they should be suspended from the surface by a heavy duty clamp. This clamp may be supported at the ground surface by beams, or it may rest on or be notched into the surface protective casing. Surface protective casing, in turn, must be supported by beams or grouted in place. The purpose of suspending the casing and screen is to insure that they remain straight and centered in the borehole. If a string rests on the bottom, it bows, preventing proper pack installation. The chart below shows a typical range of clamp sizes for various diameters, total casing, and screen weights.