An evaluation of the holding strength of three types of threaded inserts was performed. Inserts evaluated included a self tapping machine screw threaded insert, a deep thread knife edged insert and a conical flanged insert. The inserts were threaded into the end grain of mahogany, typical of use in guitar making to implement a bolt-on neck joint. Inserts were subject to increasing tension using a bolt and torque wrench until failure of the insert joint. The self tapping machine screw threaded inserts provided the strongest joint. It is speculated that strength data from tests made with homogeneous materials such as metal do not necessarily apply to wood end grain, and that coarse threaded inserts may subject the end grain to localized shear forces that result in failure of the joint.
Mottola, R.M. "Testing Threaded Inserts" American Lutherie #101, 2010, p. 54.
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