The second oldest of the double-mallet grips, the Musser grip, was invented — probably in the 1920’s — by the famous American marimba and vibraphone virtuoso, composer, conductor, teacher and instrument manufacturer Clair Omar Musser (1901 – 1998). It is the first of the non-crossed or parallel grips. In this grip category the mallet shafts never touch each other. As with the traditional grip very little, if any, documentation of the grip existed until Peter Sadlo’s dissertation Die Kunst des Schlagens in 1994. However, Vida Chenoweth seems to have written an article in 1963 for the journal Percussion called 4-Mallet Technique which perhaps deals with the Musser grip. I have at this stage not been able to find more information about the article.
The Musser grip has the inner mallet between thumb and index finger, with the middle finger’s tip anchoring the shaft end to the palm at the base of the thumb. The outer mallet is held between the middle finger and the ring finger and is wrapped with ring finger and little finger; the shaft end may protrude from the palm or is held at the end of the palm.
Among famous players using the Musser grip are for example Joe Locke (1959 -) and Daniel Berg (1971 -).
At http://www.musser-mallets.com/features/musser/ is a picture of Clair Musser using his grip in his left hand. Below are two images of my right hand demonstrating it.