Here it is – the UNIQUE and completely indispensable “RGS One Two” preparation calibration instrument! Made of high grade stainless steel from precision manufacturing by Hu-Friedy, Dr. Stevenson’s prep evaluation device will easily show you the ideal and maximum allowable extensions and pulpal depth of your class II preparations, and the incisal reduction of PFM preparations. The small end of the instrument measures 0.4 mm in diameter and 1.5 mm in length, and the larger end of the instrument measures 0.75 mm in diameter and 2.0 mm in length. Used by UCLA students and several other dental schools, this guide serves to train your eye to within 0.1 mm of ideal in your quest towards preparation mastery. Shipped in a factory-sealed protective case.