Joseph François Babinski was a French neurologist, best known for the “toe phenomenon” which he described in 1896. In 1912, he wrote a monograph in which he described two reflex hammers:
Here I will describe two which are the most frequently used. One of them is composed of a handle of nickel-plated steel which is 20-25 cm long and fixed at the center with a disk which is made of the same substance and which has at its circumference a furrow filled with a ring of rubber. In the second type, which has an advantage of being able to more easily fit into a pocket, the handle is basically the same as the first type of hammer, but the disk is replaced with a rubber ring in its peripheral canal.
There is an interesting story that around 1920 Babinski and other neurologists met in Vienna for a black tie affair. One of the neurologists present was an American by of the name of Abraham Rabiner (1892-1986). Rabiner and Babinski got into an argument over the physiology behind the Babinksi reflex. This discussion became quite heated and there was some pushing and shoving and “other nonprofessional physical activity.” Following the altercation, Babinski gave Rabiner his own personal reflex hammer as a token of support. Rabiner brought the hammer back to New York and had a modified version made in which the shaft could be screwed into the shank either perpendicular or parallel to the head. Rabiner’s version combined the best features of both hammers described in Babinski’s 1912 monograph.
Primary reference: Lanska, DJ; Neurology Nov 1989 p1542-9; The History of Reflex Hammers