Mich. Admin. Code R. 408.4263 - Threaded connections
Rule 263. Pipe connections, if threaded, shall be tapped into material having a minimum thickness as specified in table HG-370, except that when a curved surface is to be tapped the minimum thickness shall be sufficient to permit at least 4 full threads to be engaged.
MINIMUM THICKNESS OF MATERIAL FOR THREADED CONNECTIONS TO BOILERS
Size of Pipe Connection, Minimum Thickness of Material Inches Required, Inches
Under 3/4 1/4 3/4 to 1, inclusive 5/16 1 1/4 to 2 1/2, inclusive 7/16 3 to 3 1/2, inclusive 5/8 4 to 5, inclusive 7/8 6 to 8, inclusive 1 9 to 12, inclusive 1 1/4
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