Coaxial Indicators or "Coax" Indicators are excellent for alignments or determining bore centerline locations.  Designed to be used in a rotating machine spindle, the Coaxial Indicator will stay stationary while the spindle turns with the help of its restraining arm.  Because the Coax Indicator is supplied with different length contacts or "feelers", the gage is not intended for linear displacement measurement. The feeler of a Coaxial Indicator moves in an arc, so changing the length of the feeler will alter the gage's sensitivity; this is a similar situation that occurs when changing the contact point length of a test indicator.  Please contact us if you have any further questions!