Masonry Magazine May 2010 Page. 23
HWD self-drill/self-tap screw
HWD self-drill/self-tap screw with sealant washer
Screw material and finish
HEAT-TREATED CARBON STEEL is the usual material selected to manufacture the self-drilling/self-tapping screws. This process creates a hard and durable wear surface to drill a pilot hole and cut the threads in the stud. Some manufacturers' incorporate a dual heat treat process, which creates a grade 5 load-bearing surface and a good wearing surface. The lead portion of the screw is then harder for good drilling efficiency. They are excellent for durability, and embrittlement issues are abated.
The minimum finish of any screw should be zinc plating. The application of a polymer coating in lieu of just zinc can enhance corrosion protection and provide a long lasting connection.
Another cost effective selection is to use a self-drilling/self-tapping 410 stainless-steel screw. They are hardened for strength and durability, while still possessing essential alloys for corrosion protection. These characteristics will allow the screw to self-drill a precise pilot hole for the self-threading action of the screw, provide corrosion protection, and offer material strength properties that create an effective long-term fix to the steel stud. Incorporating a sealant washer will keep moisture from influencing the effects of differing material when applied to non-stainless ties.
Screw installation
Typically, a variable speed screw gun is used with depth indicating sockets to drive and seat the screw. A tool with a maximum 2,500 rpm and 4 amp power is sufficient, but not overwhelming, to create the torque and drive to seat the screw. Too large a tool will strip or snap the screw. Too small a tool will challenge labor efficiencies and risk improper setting torque (too low). This can and will make the plate assembly less than secure to the base material.
Keys to screw selection for a metal stud
Self Drilling-Self Tapping Screw
#12 Screw with a #3 point
Length no less than 2 inches
Hex Washered Head (HWH) with Sealant washer
No less the 200 pounds tension allowable
Polymer coated, or
Stainless Steel IMAS
Stephen Getz, BSCE, is president and owner of Construction Tie Products, a manufacturer and supplier of masonry ties. stone anchors, masonry restoration anchors and fasteners for the masonry industry.
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READER SERVICE #163
May 2010
MASONRY 21