While there are many varieties of gripping technologies (wedge, screw, hydraulic, pneumatic, etc.), they all can be classified as proportional or non-proportional according to the way in which the clamping force is exerted on the specimen.

Proportional Clamping Force – The clamping force exerted on the specimen is proportional to the tensile load applied to the specimen.

Non-Proportional Clamping Force – The clamping force on the specimen is independent of the tensile load applied to the specimen.