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Re: self drilling screw spacing for light gage

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Dan,

>From the AISI Specification:

The distance between the centers of fasteners shall not be less than 3d.  The 
distance from the center of a fastener to the edge of any part shall not be 
less than 3d.  If the connection is subjected to shear force in one direction 
only, the minimum edge distance shall be reduced to 1.5d in the direction 
perpendicular to the force.
(Tests have shown that screw connections loaded in shear will almost always 
exhibit edge failure when the distance from the center of the screw to the 
free edge is less than three times the diameter of the screw.)

>From the Prescriptive Method, 2nd Edition:

Screws for steel-to-steel connections shall be installed with a minimum edge 
distance and center-to-center spacing of 1/2 inch (13 mm) and shall be 
self-drilling tapping in compliance with SAE J78.  Structural sheathing shall 
be attached with min. #8 self drilling tapping screws in compliance with SAE 
J78.  Screws attaching structural sheathing to steel joists and wall framing 
shall have a min. head diameter of 0.292 inch (7 mm) with countersunk heads, 
shall be installed with a minimum edge distance of 3/8 inch (9mm).

Hope that helps!

Larry Williams
LGSEA