Distance between 2 concentric cirlces

Measure 2 circles, make a generic circle, use CIR1.R-CIR2.R as the size for the generic circle.

Assuming your picture is looking down the Z axis, create an alignment that origins X & Y on the inner circle. Next add four constructed alignment lines. These will be set to whatever workplane you are in so you need to edit each one so that one is in the XPLUS direction, one is XMINUS, one is YPLUS and the other is YMINUS (see below)



Finally construct pierce points between each of your lines and each circle so that you end up with 8 points in total - 4 sets of two points at north, south east & west positions. Set the workplane to ZPLUS and dimension the distance between each set of points. This method will allow for any concentricity error between the two circles whereas the method given by Matthew D. Hoedeman assumes they are perfectly concentric and gives a single value.

Measure both circles with the same number of hits and the same direction, at the same height.
Then calculate the 2D distance between hits.
Here, it could depends on the workplane :
ASSIGN/V1=SQRT(DOT(CIRC1.HIT[1..CIRC1.NUMHITS].XYZ-CIRC1.XYZ,CIRC1.HIT[1..CIRC1.NUMHITS].XYZ-CIRC1.XYZ))
ASSIGN/V2=SQRT(DOT(CIRC2.HIT[1..CIRC2.NUMHITS].XYZ-CIRC2.XYZ,CIRC2.HIT[1..CIRC2.NUMHITS].XYZ-CIRC2.XYZ))
ASSIGN/DIST_CIRC=ABS(V2-V1)
If there are at two different heights, then :
ASSIGN/V1=(CIRC1.HIT[1..CIRC1.NUMHITS].XYZ-CIRC1.XYZ)*MPOINT(1,1,0) if Z work plane
ASSIGN/V2=(CIRC2.HIT[1..CIRC2.NUMHITS].XYZ-CIRC2.XYZ)*MPOINT(1,1,0)
ASSIGN/DIST_CIRC=ABS(SQRT(DOT(V1,V1))-SQRT(DOT(V2,V2)))

Then use arrays as you want (average, min, max...) and dimensin it with a comment / report.

This is my go to for checking the thickness of a tube.
It isnt quite the same as checking the thickness with a pair of pin mics or something because it is just using the diameters to calculate the thickness. For a tight tolerance you might want to use JEFMANmethod or just take a point on the inside and one in the exact same locations on the outside and do a 3d distance to them in various locations

CIR1 =FEAT/CONTACT/CIRCLE/DEFAULT,CARTESIAN,IN,LEAST_SQR
THEO/<0,0,0>,<0,0,1>, 7.35
ACTL/<0,0,0>,<0,0,1>,7.35
TARG/<0,0,0>,<0,0,1>
START ANG=0,END ANG=360
ANGLE VEC=<1,0,0>
DIRECTION=CCW
SHOW FEATURE PARAMETERS=NO
SHOW CONTACT PARAMETERS=NO
CIR2 =FEAT/CONTACT/CIRCLE/DEFAULT,CARTESIAN,IN,LEAST_SQR
THEO/<0,0,0>,<0,0,1>, 6.35
ACTL/<0,0,0>,<0,0,1>,6.35
TARG/<0,0,0>,<0,0,1>
START ANG=0,END ANG=360
ANGLE VEC=<1,0,0>
DIRECTION=CCW
SHOW FEATURE PARAMETERS=NO
SHOW CONTACT PARAMETERS=NO
ASSIGN/ V1= (CIR1.D.MEAS-CIR2.D.MEAS)/2
F1 =GENERIC/LINE,DEPENDENT,CARTESIAN,$
NOM/XYZ,<0,0,0>,$
MEAS/XYZ,<0,0,0>,$
NOM/IJK,<0,0,1>,$
MEAS/IJK,<0,0,1>,$
DISTANCE/ V1,V1
DIM LOC1= LOCATION OF LINE F1 UNITS=IN ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH HALF ANGLE=NO
AX NOMINAL MEAS +TOL -TOL DEV OUTTOL
L 0.5000 0.5000 0.2000 0.2000 0.0000 0.0000 ----#----
END OF DIMENSION LOC1

Hey man, thank you so much for this! I've been searching these forums for almost two weeks trying to figure out how to measure an O-Ring depth. This has been the only answer that actually worked for me!

how do you use "cir1.r-cir2.r" for the size for the generic circle?

use an assignment assing/V1=cir1.r-cir2.r Then create a generic feature using V1.