PrepSure Classic Colors Crown Prep Guide Red- 1.5mm 3/Pk. Double-Sided crown preparation instruments to monitor occlusal, distal, and mesial clearances for crowns and onlays. Indicated for PFMs, zirconia, and other layered crown materials. Autoclavable (steam heat only, no dry heat, up to 270°F for 10 minutes at 30 psi max).