Here is a diagram of the "Unified" (Block II) command module hatch. It is referred to as a "unified" hatch because it incorporates both the outer heat shield hatch and inner crew compartment pressure hatch in a single hatch. This hatch was initially flown on Apollo 6.

Additional information on the Block II hatch, with an emphasis on the changes from the Block I hatch, can be found in "The Apollo Command Module Side Access Hatch System", located in the Proceedings of the 4th Aerospace Mechanisms Symposium (page 157 in the report, or page 166 in the PDF). The paper includes photos of the hatch installed in the command module.

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From p. 37c (p. 57 in the PDF) of Apollo 8 Press Kit [direct link to 4.3 meg PDF] from the heroicrelics mirror of the Kennedy Space Center Library press kit page.
Extraction and cleanup by heroicrelics.