The provision of satisfactory grips for holding dumb-bell specimens in tensile testing machines has always presented a number of difficulties. Several styles of self-closing grips are available, but none has been regarded as entirely satisfactory. Thus, the cam type is clumsy and often fails to hold the test-piece at very high extension or when the surface of the rubber is covered with a wax bloom, as sometimes happens. Another type, the bar grip, illustrated in Figure 1, has very much better holding power, but requires the specimen to have undersirably long end tabs.
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