This 3mm thick rubber foam pad can replace the leather pad on any wooden Mach One shoulder rest for 4/4 violin. This includes the standard Mach One or hook mode. To apply, simply pull off the leather pad. Some glue residue can remain on the rest. Remove the backing and press the foam pad firmly onto the rest. It can also be applied over the rubber pad of the M07 Shoulder Rest, but not on other plastic models or viola rests.