Pentax 645 Operating Manual page 11

Attaching;
1. Loosen the grip lock screw. As indicated in the
photographic illustration, align grip holes on the
grip with the corresponding pins on the side of
the camera.
2. Push up the grip until it engages with an audible,
click, signifying correct contact.
3. Turn the grip locking screw located on the
bottom, in the direction of the "LOCK" arrow
designation, using a coin or a similar tool.
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