Designing with Threaded Inserts
Threaded inserts are designed to create greater clamping pressure between a base material and a mating component using a standard machine screw. To better use the load-bearing capacity of high- tensile-strength machine screws, designing for threaded insert performance involves three considerations:

• Proper specification of mating components to avoid unnecessary forces between the threaded insert and the base material.
• Sufficient base material wall thickness to support the threaded insert.
• Proper hole dimensions.

The performance of threaded inserts is usually measured in terms of the axial or torsional forces required to shear the threaded insert from the base material. Pull-Out Resistance is the axial force required to pull the insert free of the base material, and Torque Resistance is the axial torque required to twist the threaded insert free of the base material. See fig. 5a and 5b.

Proper design for threaded inserts involves creating axial clamping forces on the threaded insert while minimizing excessive torques and jacking forces. See fig. 5c.

Measure of Performance

5a	5b	5c
Pull-Out Resistance Axial force applied to mating fastener which causes threaded insert to shear from base material.	Torque Resistance Excessive torque applied via mating fastener which causes threaded insert to twist in base material.	Jack-Out Resistance Indirect measure of pull-out resistance. Torque applied via mating fastener through stepped washer which causes threaded insert to “jack” or shear from base material.

Design of Mating Components
The threaded insert should be installed perpendicular to the surface of the base material so that the forces on the insert are axial. Mating components should be mounted flush to the surface of the base material to minimize the effects of uneven or rotational forces. To minimize jacking forces, holes in mating components for fasteners should be large enough for the fastener but smaller than the diameter of the threaded insert, and fasteners should not contact the base material when fully installed. See figure 6 below.

6
Do: Mount threaded insert perpendicular to surface. Flush mount mating components. Specify access holes for fasteners smaller than insert diameter. Specify proper length fastener to avoid contact with base material.	Don't: Create unnecessary forces between mating part and insert. Create jacking forces with access holes larger than insert diameter. Create jacking forces with mating fasteners.

Boss Diameter
To properly support the threaded insert, there must be sufficient material around the threaded insert. This is usually specified in terms of a minimum wall thickness or minimum boss diameter. When considering inserts installed near the edge of a part, minimum wall thickness is defined as the minimum thickness of base material around the drilled or molded hole for the threaded insert. In soft metal base materials, the minimum wall thickness should be 25% to 50% of the threaded insert diameter. In plastics, the minimum wall thickness should be increased to be 50% to 100% of the threaded insert diameter. When considering circular bosses, the minimum boss diameter should be the diameter of the threaded insert plus two times the minimum wall thickness (fig. 7).

Minimum wall thickness (W) and minimum boss diameter (BD) are important parameters for performance of threaded inserts. They are also key factors in avoiding bulges or sink marks on the outside surface of the component. Minimum boss diameter is twice the minimum wall thickness plus the maximum diameter of the threaded insert.