Standard Torque Specs for Machine Screws

Written by tamara wilhite
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Standard Torque Specs for Machine Screws
Machine screw torque standards depend on size, material and application. (screw image by Alison Bowden from

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 organisations 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 136 Kilogram while 5/8 inch machine bolts and screws can withstand 1678 Kilogram.

International Standards

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.

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