Nikon SMZ800N Instruction Manual page 46

 Anti-drop collar
An anti-drop collar is supplied with the focus mount. When
using a focus mount attached in the middle of the support
pillar, be sure to attach the anti-drop collar under the focus
mount so that it fits.
* A C-LSL2 LED Epi Illuminator 2 can be attached to the
C-FMCN Focus Mount via an SMZ-U Epi Arm or a G-EIA
Flexible Arm.
* A nosepiece can be used together with a zooming body
combined with a C-FMCN Focus Mount.
Chapter 4
Functions and Operations of the Devices
Anti-drop collar
32
Anti-drop collar