Extension bars play a supportive role for ratchet wrenches and sockets. However, they often come with various ingenuities in their details.

The bar on the left end in the picture below (Picture 1) was made by U.S. tool manufacturer Snap-on in 1942. It carries a simple hole that accepts a 3/8-inches rectangular shape. Its interior is made of flat surfaces with a small round hole for a handle to snap in when it is inserted. The two bars next to it, one from the U.S. maker Craftsman and the other from Snap-on, have extra beveling added to improve the fitting. Next, at the center of the picture, is the bar made by the Japanese tool maker KTC. It is a standard type of extension bars as it has a recess deep inside the bar. The one to the right of it is a product of NEPROS, KTC’s highest-grade product line. It has a round hole instead of a square one to prevent the stress concentration. Each of the two products on the right end, one from the U.S maker Kobalt and the other from Craftsman, has a dent on the near end of the hole, which helps to fix the handle moderately if it is inserted lightly while holding it steadily when it is inserted deep inside to prevent it from coming off. Because both of them were developed under the American DIY shop brands, they apparently needed extra features to be regarded as products with differentiated values.

Extension bars basically have square holes at one end, but the other end is designed to provide a barrel-shape joint that allows for a bit of movement called “wobbling.”

In addition, a universal joint is available if more wobbling is needed. Its double axes enable free and flexible bending. The bar on the right side in Picture 3, a Nepros-brand one, provides stable rotation movement with little wobbling as its two axes cross at one point. Presumably, cost- and intensity-related problems may have stood in the way of realizing such movement. But as we see in these products, technological evolutions will likely open up further possibilities to improve industrial tools.

Takeyoshi Mugikura
Product Design Dept.
Senior Director