Indicator base for measuring deck height. This is just for the base no indicator is included. Base has a 3/8 hole to take a standard 1” travel indicator with a 3/8 stem. Insert indicator, snug set screw. Zero on a precision flat surface. Indicators can cost $10 to $100 plus, personally for this purpose I use the cheapo indicators, for deck height measurement you don’t need a high dollar indicator. Base is 4” wide so it will work on 99% of aircooled VW engines out there.