Assign to ObjectsThese settings also appear on right-click context menus for the thumbnail previews and the thumbnail background.
Assign to ObjectsAssigns the current material to selected objects.
Assign to Layers of ObjectsAssigns the current material to the layers of selected objects.
Assign to Layers...Assigns the current material to selected layers.
Select Object(s)Select objects that use the current material.
Create New MaterialCreates a new material from a template.
Save to FileSaves a material to a Rhino .rmtl file.
CopyCopies the selected item to the Clipboard.
PasteCreates a new item based on the contents of the Clipboard.
Paste as InstanceCreates a new item based on the contents of the Clipboard. The new item will be linked to the original item.
DeleteDeletes the selected item.
Select all items in the list.
So you can change the common settings and thumbnail properties of all items.
Reset to DefaultsChanges all of the item settings to the default.
DuplicateCreates a new item from the selected item.
Tags...Pops up the Render Content Tag dialog to manage tags. Tags group or categorize items to make searching easier.
Filter By TagsHides the items that don't have the selected tags.
Sort AlphabeticallyLists the items with their names in ascending (A to Z) order.
Remove InstancingRemoves the connection between instanced items.
Update Preview NowUpdates the preview of the selected item when auto-update is disabled.
Floating PreviewFloats the preview image in a resizable window.
Floating EditorEdits the selected item in a separate dialog.
Sphere
Cube
Cone
Pyramid
Torus
Plane
Scene
Show LabelsDisplays thumbnail name labels when in Grid mode.
List mode always displays labels.
Show UnitsDisplays the dimension of the object in the preview.
The object dimension can be changed in Preview Properties.
Auto-Update PreviewAutomatically updates all previews as settings change.
Update All PreviewsUpdate previews manually when Auto-Update Preview is off.
PropertiesOpens the Preview Properties dialog box.
Preview thumbnail images and the background area between thumbnail images both have context menus.
Preview Properties
The preview properties settings control the appearance of the thumbnail images.
Specifies the shape of the object that displays the material in the preview thumbnail.
Sphere
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Pyramid
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Cube
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Torus
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Cone
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Plane
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Scene
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Sets the dimension of the preview object in meters.
Controls the appearance of the thumbnail background.
The default gray environment is used.
A gray checkered backdrop is used.
Uses an environment as the background. 
Select an existing environment or create a new one.
The list of existing environments.
Create a new environment.
Controls the right-mouse drag object or camera rotation.
Right-mouse drag rotates the object.
Right-mouse drag rotates the camera.
Sets the horizontal rotation angle for the object or camera.
Sets the vertical rotation angle for the object or camera.
Uses the default lighting.
Uses the current skylighting settings.
Saves the thumbnail properties as the default settings.
Uses the default settings.
Closes the large preview pane.
