Mitutoyo Surface Roughness Deep Groove Detector The Standard Detector for the Mitutoyo Surface Roughness Tester models SJ-210 & SJ-310 has a measuring tip that is about 2.4mm tall. To be able to measure the surface roughness of a groove that is taller than 2.4mm, Mitutoyo recommends using the Deep Groove Detector for the Mitutoyo Surtest models SJ-210 & SJ-310. This Deep Groove Detector has a measuring tip that is only 2mm wide and 10mm tall, allowing you to measure the surface roughness of deep and skinny grooves. Features include... Deep Groove Detector for Mitutoyo Surftest Models... SJ-210 SJ-310 4mN Measuring Force Stylus Profile: 5 umR / 90° Tip Radius 0.39" / 10mm Deep Stylus 0.08" / 2mm Wide Stylus