Tool base is billet alum. that is 9.250" long by 1.00" wide, indicator has 1.00" travel and reads in .001" increments.
For a video on how to use this tool check out on You Tube B&J Racing Transmissions - Clutch Pack Clearance Set-Up
This educational video shows step by step how to set up the clearance on the clutch pack.
As noted in the video the clearance should be between 0.055" - 0.065" for the Front Case and 0.065 - 0.075 Rear Case for optimal performance.
You can also copy paste this link in the You Tube search box and watch Mike work his magic. https://www.youtube.com/channel/UCAoL8FGvt8dHu2XrxaSSGjA