Ask HiltiAskLearnArticles
Ask Hilti

Self-drive screw member thickness

Posted by Wang Bo-Shiuan (Shawn)about 4 years ago
Self-drive screw member thickness

I would like to connect 5/16" PL to an existing plate which is 3/8" thick, slightly thicker than drilling capacity. Look from the data sheet 3.6.4.5 S-MD 5/16-24 WHW has the maximum drilling capacity of 5/16", does this mean I can't use self-drive to attach PL to the existing plate? It also mention the maximum thickness is 0.85" which is larger than the combined thickness of both plate. What does these two number mean?

Thickness,drilling capacity,self-drive screw
1 Reply
Posted by PARIS STANTONabout 4 years ago
Hilti Verified

Hi Shawn,

The maximum drilling capacity is the metal thickness the self-drilling screw head can drill through. However, the maximum total thickness (MT) describes the maximum thickness of all attachments to be fastened plus the base material. The maximum total thickness (MT) for all screws is the length of the threads reduced by the first three threads (protruding past the back-side of the base material). If the thickness is greater than the maximum drilling capacity but within the maximum total thickness, the installation will typically require predrilling.

Regards,
Paris

drilling capacity,self-drilling screws,total thickness
2 comments on this reply
Posted by PARIS STANTONabout 4 years ago
Shawn, Customers in the past typically pre-drill a 1/16” hole smaller than the diameter of the screw/fastener shank. Regards, Paris
Posted by Wang Bo-Shiuan (Shawn)about 4 years ago
Hey Paris, Thank you for response. Further question about pre-drilling. Is any reference for how to do the predrilling? I imagine the clamping force is from the threads that self-drilling screw carving through the connecting members. Shall pre-drilling approach drill a smaller hole then designated diameter and then drive the self-driven screw through hole to enlarge it? Or recess some thickness and drive the self-driven screw to the rest of thickness which is less than the drilling capacity? Thank you very much. Best Regards, Shawn