Origins of the Modern Socket Wrench

Modern socket wrenches in use today have been an evolution over time. We have come a long way from the true, flat hexagonal, six sided, sockets of our grandparents era.

In order for a socket to fit over a fastener, there has to be a slightly larger geometry of the socket. This slightly larger geometry allows the socket to slide over the fastener, and then with rotation, the socket contacts the fastener, and a rotational force can be applied. The traditional hex sockets were prone to stripping the nut or bolt head because the forces were typically applied directly to the corners of the fastener. With the fasteners converging to a point at the corners, the material becomes increasingly thin, and weaker than the flat face of the fastener. It is easy to see that applying a rotational force to the weakest part of the face will lead to a greater number of stripped fasteners.

To improve on the socket design and decrease stripped fasteners, engineers turned towards the development of a corner radius. Each inside corner of the socket was extended slightly past the dimension of the fastener through the introduction of a small recess and an angle of the socket face that moves slightly away from parallel of the fastener face. This combination of corner radius, plus the slightly divergent angle allows the socket to make contact with the fastener away from the sharp corners of the fastener. With the force applied further away from the corner of the fastener, more force can be applied without stripping it.

Michel Dossier in 1984 made a patent application, eventually assigned to Facom SA, wherein we see the beginnings of the radius corner design (US4581957 Fig.2).

US4581957-drawings-page-3
Radius corner improvement to wrench design. Michel Dossier 1984

In 1991, Richard Wright and Theodore Vozenilek of the Wright Tool Co. began the patent application process for the radius corner design discussed here. You can see from the patent application images the design features incorporated (US5284073A, Fig.1 and Fig.2). That patent application was finalized with a grant of patent in 1994, and expired after its lifetime in 2011.

Around the same time, William Mader and Peter Peppel filed an application for patent in 1991. Their design would eventually be assigned a patent to Easco Hand Tools Inc.. This patent application was for a wrench design that improved on the one patented by Michel Dossier.

Wright Tool Co patent US5284073
Radius corner socket wrench improvement. Writght Tool Co. 1991
Wright Tool Co socket wrench design patent 1991
Wright Tool Co socket wrench design patent 1991

Most modern sockets on the market today have incorporated the corner radius design. That’s because the original patents protecting the intellectual property belonging to Wright Tool Co. and those who came before them have expired, and moved into the public domain. As a result we all benefit from their innovation and hard work.

In a more recent patent application by Snap On Inc. in 2013, the inventors of a further modified design reference the patent application of Richard and Theodore, citing the current standard, referencing an image of “…the present application in engagement with a typical hexagonal bolt head or nut.” (US 201050135910A1Fig. 1)

Snap On Inc reference to Wright Tool Patent
Snap On Inc. reference to socket wrench design improvements. 2013

So the next time you reach for a hard-gripping impact socket to knock loose a corroded bolt, be sure to think about the hard working engineers that believed there was a better way. Our hats are off to you, thank you for bringing your inventions into the world to make our jobs easier.