Black Granite Indicator Stand includes column and Special Clamp. The Special Clamp is designed to hold indicators by their stem. The clamp works with indicators with a 3/8" diameter stem (most inch reading indicators), but you can also use an 8mm bushing with the stem clamp to hold metric reading indicators that have 8mm diameter stems as well.The 4.75" throat clearance is from the column to center line of indicator stem. Features include... 18" x 24" x 3" Black Granite Base AA Grade: +/- .000037" Overall Accuracy 1.365" diameter post 10" tall post 4.75" Throat Clearance Special taller posts available upon request.