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Distributor's Link Magazine Summer 2018 / Vol 41 No3


172 THE DISTRIBUTOR’S LINK MICHAEL MOWINS FASTENER HEAD STRENGTH WHITE PAPER from page 114 FULLY THREADED HEAD STRENGTH RATIO DIAGRAM The calculation of the Head Strength Ratio then becomes a comparison of the Stress Cone effective tensile area with the full shank diameter for a bolt or the thread pitch effective tensile area for a fully threaded screw. Ideally the Head Strength Ratio will always be 1 or greater so that a tensile failure of the fastener will always be at or above the minimum tensile strength of the thread pitch diameter. This assures that there is enough strength in the head to shank juncture to avoid “popping” the head off the fastener and failing the joint. The diagram above shows the tensile stress areas (shaded areas) in the thread profile and in the head to shank juncture area for a fully threaded fastener. Note in the head cross section that the stress area goes from the under head diameter that is approximately the thread pitch diameter to the nearest point of the bottom of the recess. In this case the recess is actually cruciform in the cross sectional area nearest to the head shank juncture. For the purpose of comparison with other recess fastener drive systems we will ignore the minute amount of added material between the wings of the recess and only use a circular area based on the outer diameter of the wings at the cross section. Calculating the Head Strength Ratio: Now that we have an agreed upon set of criteria that we will use for the calculations it is important to select whether the minimum or maximum of each dimensional variable should be used to determine the “worst case” scenario in which head to shank failure is most likely at levels below the thread pitch effective diameter tensile failure levels. We have already determined that for a fully threaded fastener the cross sectional area under the head is determined by the blank diameter and that for a fastener with a full body the larger body diameter will be used for the calculation. We should therefor use the minimum under head diameter as the base line for the calculation. Looking at the following diagram it is easy to see that the maximum recess depth should be used as the base line for the calculation since it yields the smallest cross sectional area between the blank diameter and the nearest intersection with the recess. Typically, fully threaded fasteners are not used in critical applications and in these circumstances it is often acceptable to allow a Head Strength Ratio that is less than 1.0 based on analysis of the application. CONTINUED ON PAGE 182

THE DISTRIBUTOR’S LINK 173 Suncor Stainless is looking to expand their line of cast shackles to offer their customers an even larger selection. They announced their new shackle program with added styles and new sizes. Suncor introduced the Bow Shackle with Captive Pin in sizes ranging from 5/32” to 15/32”, the Long D Shackle with No Snag Pin in sizes ranging from 1/4” to 1/2”, the Twist Shackle with Captive Pin in sizes ranging from 1/4” to 3/8” and the Twist Shackle with No Snag Pin in sizes ranging from 1/4” to 1/2”. “We took a long look at the styles and sizes of cast shackles that we were offering and agreed that we could add more” says David Morgan, Vice President of Sales and Marketing for Suncor Stainless. “We wanted all of our cast shackles to come in a variety of sizes along with options of screw, captive and no snag pin styles for each body type.” Suncor is also looking to save their customers some money as well as ship product faster and reduce backorders. They will be offering volume discounts on cases along with duel inventory maintenance which will allow large quantities of shackles to be stocked in both Plymouth and Las Vegas warehouses. This will make product readily available with little wait time to meet the increasing demand. Suncor Stainless, Inc. is a leading manufacturer for stainless steel hardware in the industrial, marine, government, architectural, OEM and commercial industries. Suncor’s modern facilities manufacture the highest quality stainless steel chain, wire rope assemblies and custom parts. The in-house capabilities include a product development staff whose tireless efforts, along with valuable input from clients, work to continuously improve and perfect their ever-expanding product line. For more information contact Suncor Stainless at 70 Armstrong Road, Plymouth, MA 02360. Tel: 1-800-218-7702, Fax: 508-732-9798, Email: or visit them online at


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