Williams (round) Probe 1-2-3-5-7-8-9-10 mm marking with #23 Shepherd’s Hook Explorer The thin, unbreakable, yet flexible tips from a special steel alloy guarantee an extremely long life They are efficient at reaching interproximal areas and testing tooth enamel. Expro tips are made from spring tempered stainless steel and machine ground to exacting tolerances Expros combine an Explorer tip and a Probe tip into one easy-to-use double-end instrument Williams / 23 Probe 1-2-3-5-7-8-9-10 mm markings with #23 Shepherd’s Hook Explorer.