In the preceeding reports the authors discussed the effect of crack arresting action of several kinds of crack arrester model with the application of two dimensional elasticity theory of cracked plate. Numerical calculations and some preliminary experiments showed that the brittle crack propagstion arrest could be explained by a relatively simple fracture mechanics criterion based on Kc-concept. In this report, a further experimental check was made by large size brittle propagation-arrest test (Double Tension Test) using specimens with patch and rivetted stiffener type crack arresters. The method of analysis described in the previous report was applied to the test results obtained. The experimental results showed good agreement with the estimations from analytical calculations. This verifies the adequacy of the above-mentioned criterion, and provides fracture mechanics interpretation of brittle fracture propagation test and a quantitative approach for brittle crack arrest mechanism and design of crack arresters.