According to “Automotive Technology: A Systems Approach, Volume 2” by Jack Erjavec, the correct torque provides the tightness and stress the manufacturer has found to be the most desirable and reliable for a given screw or bolt. Bolt strength recommendations are often given in installation and assembly instructions. Bolt strength is also provided by machine screw manufacturers and international standards organizations like the American Society of Mechanical Engineers (ASME).
Machine Screw Types
Erjavec states that machine screws are similar to cap screws but have a flat point; machine screws can have a round, flat, Torx, oval or fillister head. “Do It Right The First Time” by Gene and Katie Hamilton says that when it comes with nuts, a machine screw is called a stove bolt. Machine screws can be torqued with a standard tip screwdriver
Standard Torque Specifications
Machine screw torque specifications vary based on the type of material from which they are manufactured. According to “Pocket Ref” by Thomas J. Glover, #2 yellow brass machine screws have a standard torque of 2 inch pounds while silicone bronze machine screws are to be torqued to 2.3 inch pounds. “Fasteners Handbooks” by Julius Soled states that the maximum safe working load for 3/16 inch machine bolts and screws is 300 pounds while 5/8 inch machine bolts and screws can withstand 3,700 pounds.
ASME Standard B18.6.3 provides the standard torque specifications for No. 0000, No. 000 and No. 00 machine screws. The American Society for Testing and Materials (ASTM) Standard F738M provides further guidance on recommended torque standards for different types of machine screws based on their size and material.
- “Automotive Technology: A Systems Approach, Volume 2”; Jack Erjavec; 2004
- “Do It Right The First Time”; Gene Hamilton, Katie Hamilton; 2005
- “Fasteners Handbooks”; Julius Soled; 1957
- “Pocket Ref”; Thomas J. Glover; 1999
- ASTM F738M - (2008) Standard Specification for Stainless Steel Metric Bolts, Screws, and Studs
- Photo Credit screw image by Alison Bowden from Fotolia.com
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