The American musician and stamp collector Lem Leach became in the late 1940’s Mike Mainieri’s vibraphone teacher and it is through Mike that this grip is preserved. Also, it is this grip that is the basis for the Mainieri grip. If documentation is weak for most grips it is most likely non-existing for the Leach grip. Lem Leach was an alcoholic at the time Mike Mainieri (1938 -) started taking lessons from him and the instruction Leach gave was not very detailed. However the following description is based on what Mainieri wrote to me in an e-mail conversation about the grip in 2011.
The Leach grip is a non-cross grip with the inner mallet in the normal place between thumb and index finger. It is, though, held with the outer phalanxes of both fingers instead of the usual outer phalanx of the thumb and the middle phalanx of the index finger. The shaft-end is at the rear end of the palm and the middle finger is holding the shaft against the palm at the base of the thumb. The outer mallet is placed between the ring finger and the little finger and the little finger is wrapped around the shaft and assisted to stay in place by the ring finger. The outer mallet shaft is, like that of the inner mallet, held with its end at the rear end of the palm.
I am the only player I know of that is using this grip since Lem Leach. However, there is a picture in Mark Andreas Giesecke’s and Wessela Kostowa’s book Compendium der 4-Mallet-Techniken that is meant to depict the Mainieri grip but actually has more similarities with the Leach grip. Below are pictures of my right hand demonstrating the Leach grip.