My experience has been that it varies in my area depending on the mill. (Florida/SE Georgia)
These two sites describe chip and saw. The first is Mississippi and informative. The second is Georgia Pacifics requirements for Alabama, Georgia and Florida and includes listings of some of the mills.
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http://msucares.com/pubs/publications/p1777.pdfStraight, clear stems with diameters from 8 to 14 inches can qualify for chip-n-saw
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http://www.gp.com/forestry/southern.htmlClaxton, Ga. Contact: (912) 739-4803, Joe Cheney
Cross City, Fla. Contact: (352) 498-7140
Palatka, Fla. Contact: (904) 325-7582
Warrenton, Ga. Contact: (706) 743-8034
Pine Chip-n-Saw Wood Specifications:
Species: all Southern yellow pine including loblolly, longleaf, shortleaf and slash
Large-end diameter: min. 9" and max. 16"
Small-end diameter: Ranges from min. 4" to 6"
Lengths: most mills accept tree-length; for cut-to-length requirements, please call individual wood procurement offices listed here.
DBH: 9" min. diameter at breast height
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I hope this is helpful
tom