Sheet metal screw manufacturers recommend torque. The ideal torque for a sheet metal screw will securely hold the two items together without damaging the screw or warping the sheet metal.
The proper torque will also keep the sheet metal screw tightly. Drive sheet metal screws through a hole slightly smaller than the screw diameter.
According to "Collision Repair and Refinishing," "when the screw is driven into the punched hole, the metal driven through when punched is pulled back by the metal screw. This makes the bond tighter and stronger than if the hole is drilled".
Factors Affecting Torque
Sheet metal screws require more torque to go through hard material than soft. Thicker sheet metal requires more torque than thinner sheets.
Torque requirements decrease as the prepared hole size approaches the diameter of the sheet metal screw diameter. Steeper screw pitches require more torque to insert.
About 10 percent more torque is required to remove the screw from wood than is required to insert it.
Determining Maximum Torque
Tightening torque can be any force between the thread stripping torque, when the sheet metal screw's threads are stripped from the bolt, and above the maximum tapping torque. The maximum torque a sheet metal screw can receive when being driven into particle board is 136 times the density of the particle board plus 2798.
The resulting value in inch-pounds equals the maximum torque that can be applied to the fastener. For metric units, the maximum torque will be 00096 multiplied by the density of the particle board plus 316.
This will give the maximum torque in Newton-meters.
American Society of Mechanical Engineers (ASME) standard B1864 is the self-tapping sheet metal screw torque testing standard. ASME B1864 is the standard process for determining the maximum torque a sheet metal screw can withstand.
The American National Standards Institute (ANSI) has adopted this standard. American Society for Testing and Materials (ASTM) International standard A548 was the specification for tapping or sheet metal screws.
ASTM A548 has been withdrawn without a replacement.