Starrett AGD Indicator Hole AttachmentProduct ID:
This hole attachment enables your dial indicator to measure the inner surface of holes just like a test indicator.
Both models have a 0.375 inch diameter hole to attach to all indicators made to AGD standards. The contact ball end on the swivel arm is 1/8 inch in diameter.
Model 670A has a measurement range of 0-0.375 in.
Model 670B has a measurement range of 0-0.5625 in.