ASTM C1202 applies for cylinder specimens that have a nominal diameter ranging from 95 to 100 mm. If the end-user has a sample smaller than 100 mm, he can use epoxy around the rubber gasket. The epoxy should be placed where the gap/space is located. The intention to use epoxy is to seal the test cell from leakage. In addition, as long as all gaps are closed, the test can be performed without any further issues.   If the specimen is not 95 mm in diameter, you must adjust the results based on the diameter of the sample tested according to ASTM C1202 section 11.2.