Liutaio Mottola Stringed Instrument Design

Woodworkers' Popup Units Conversion Tool / Calculator

Calculator converts to/from decimal inches, fractional inches, millimeters. Popups must be enabled for this site. From the Liutaio Mottola lutherie information website.

Did you know ....

.... you can click on most of the assembly photos on this site to enlarge them for a close look? Also, hovering the cursor over most linear dimension values will convert the values to decimal inches, fractional inches, and SI units.

Testing Threaded Inserts


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.

Reprints of this paper can be ordered from the Guild of American Luthiers.