Trimming lines with circles or ellipses

I drawning 2 circle as radius 250mm.the  distance between two circle is 0.08mm I drawing one line segment between two circle and I Expanding line segment as length 20mm.then I offset this line The amount 2.5 mm in vertical side up.

When I trim these horizontal line that are Cross-Being with two circle the Remaining line segment is shorter than real distance between two arcs I thinks its happening?

Also I attached 7 pics I try show my problem.

Also when I want obtain horizontal distance with distance command or by linear the intersection is not start from circumference.

Please help me whats this and how I can get real  horizontal distance between two arcs

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