There are in essence two types of tensile grips:
- 'Self-tightening’ whereby the clamping force to hold the specimen increases as tensile load is applied. This is achieved by the action of wedges, levers, eccentric cams /rollers and pincer-scissors, which all move to tighten their hold as tensile load is applied during the test thereby reducing the risk of slippage.
- ‘Side-action’ whereby the clamping force to hold the specimen is independent of the tensile load applied. The clamping force is achieved by parallel jaw faces which are set to a certain position by a screw-action or via pre-loaded springs. As the specimen decreases in thickness when it is stretched during the test there is a commensurate reduction in clamping force exerted by the ‘fixed position’ parallel jaw faces potentially increasing the risk of slippage. Such grips are ‘screw-action’ Vice Grips, Pinch Grips, Toggle Grips, Claw and Chuck Grips.