This listing includes both the hex key holder and a matching lower rail stop for the NN3 MK3 or NN6 panorama heads, designed to be attached to NN3 MK3 or NN6 lower rail.
The hex key in the holder is meant for adjusting the standard camera plate screws for attaching camera on the upper rail. This holder makes the hex key available on the go. Lower rail stop is designed to remember the no-parallax point on the NN3 MK3 or NN6 lower rail.
You can also purchase these two items separately (F6031 and F6044).