Face and grip selection is a very important factor. By not choosing the correct
set up, your specimen may slip or even break inside the gripped area ("jaw break").
This would lead to invalid results. The faces should cover the entire tab or area
to be gripped. You do not want to use serrated faces when testing materials that
are very ductile. Sometimes covering the serrated faces with masking tape will soften
the bite preventing damage to the specimen.