Fowler High Precision The 54-420-302-0 Fowler Parallel Chisel Probe for X-Pro .0004" is on sale at Gaging.com. Measure Smarter! For gaging sharp edges or small O.D.s where probe is perpendicular (in 90° or 270° position) to axis of traverse. 90° diamond chisel stylus, 0.0004"/10?m radius.