Audio craft AC 3300 on fly VTA

CORRECTION:

Actually, the AC-3300 also comes with a lightweight arm base option for suspended table, the arm base model # CB-3040LB. Perhaps your arm is equipped with the lightweight arm base.

It looks like the arm comes in two flavours with and without a micrometer. At the same time it looks like both have the same model number.

The AC-3300 comes with micrometer and the AC-3000 without it.

Was the micrometer an optional accessory and what is the proper model # for it?

AC-3000 can be upgraded with micrometer by replacing the center block model # CB-3040.