#142 - Extra heavy plexiglas. These plastic tools will positively not bum or blacken interior finish. Sharp corners.
#144 - Will not dig or gouge. Sligtly rounded edges. Will give long life and service at reasonable cost.
#170 - Flexible corners, just the right degree of resilience to work well, back covered with a stiff industrial rubber. Reinforced with thin, rubber-covered aluminum plate.