Six Boring Heads are included in the "S" Series in three basic sizes - 1-1/2? This is the S 1-1/2. The S-1-1/2 comes with 1/2? As in all Criterion Heads, with the exception of the No. S-1 - these head shave threaded backs that will accept a variety of shanks.
The micrometer adjusting screws are direct reading with 50 graduations on the dial of the No.