The double capstan grips can be used to grip filamentary, high-extension tensile specimens.
With this deflection principle a force differential occurs over two stages, allowing specimen failure within the gauge length with no jaw breaks.
After the deflection of the double thread, a prestress weight (not included in scope of delivery) is attached. During this phase all three rollers can be moved to compensate for the change in length caused by the attachment of the pre-tension weight. The three lengths are adjusted to the material being tested.
Finally, the double thread is also gripped in height adjustable specimen grips.
After closing the specimen grips, the deflection rollers are locked into place. This results in frictional forces between the rollers and the specimen, which gently reduce the tensile force prior to end clamping (specimen grip), ensuring that the specimen is gripped securely and prevents the jaws from breaking.
A specimen grip with constant gripping force is used to clamp the double thread because the specimen to be tested can frequently slip out from between the gripping areas.