This S-3 Boring Head is the forerunner of all Criterion heads. With the exception of the bar holder, this unit has changed little in the past 60 years. Its practical simplicity and proven performance have consistently made it a big seller in our line. The advantages of a square design are seen in the extremely wide base and the 1"" hole capacity for boring bars and tools. The latest improvements are a cone-shaped bar holder and the addition of a direct reading dial screw. A 1-1/2-18 threaded back permits the use of any of the 1-1/2-18 threaded shanks listed in the V-Flange & BT Shanks and the Shanks & Adapters sections.