Section 6.3 of ASTM B470 covers the mandrel test for Type III (heavy bonding) bonded copper conductors. The conductor is wrapped six close turns over a mandrel of size specified in Table 3.
After wrapping, the conductor is slipped off the end of the mandrel for examination. No separation of strands shall be visible to the unaided eye.
The mandrel diameters range from 3/16 inch for AWG 16 to 1/32 inch for AWG 24 and 26. This test verifies that the heavy bonding process creates a sufficiently robust connection between strands to maintain conductor integrity during wire processing and installation.