With three grooves, they should be 120 degrees apart. If the bore is 0.349, measuring as you show, between the center of the bottom of a groove and the land directly opposite it, should give 0.354, not 0.349, for a 0.005 deep groove. The measurement would have to be from one land to another to give 0.349. If the grooves each do not span more than 60 degrees, there will be locations, 90 degrees or so from the centers of the grooves, where lands will directly face each other. Measuring from one land to another here would give your measurement of 0.349.
With care in choosing your locations, you should be able to both measure from land to land and from bottom of groove to land.

Last edited by vangulil; 11/05/16 06:23 PM.