Summary

These brackets slide onto the bars holding the back of the amp and prevent the amp from moving side to side.

Made for http://www.musiciansfriend.com/accessories/musicians-gear-deluxe-amp-stand and an inner length of 430 mm between the inside walls of the amp's speaker compartment (in this case a Line 6 Spider IV 75).

This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/dJcWYHSjPFs