Check the hardness of clay-like materials, the burst strength of plastic coverings, etc.

Imada PG-2 (2mm, 44 lbf capacity)
Imada PG-3 (3mm, 44 lbf capacity)
Imada PG-4 (4mm, 44 lbf capacity)
Imada PG-5 (5mm, 44 lbf capacity)