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. This 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.