? Model S Square Style ? Six Boring Heads are included in the "S" Series in three basic sizes - 1?1/2", 2" and 3" square. The S?1?1/2 and S?2 come with either a 3/8" or 1/2" hole while the S?3 has either 3/4" or 1".As in all Criterion Heads, with the exception of the No. S?1 - these headshave threaded backs that will accept a variety of shanks. The micrometer adjusting screws are direct readingwith 50 graduations on the dial of theNo. 1?1/2 and No. 2 and 100 on the No. S?3.