What is .XLB file?
Stores custom settings for toolbars (also known as command bars) created in Microsoft Excel; toolbar settings can be modified within Excel by choosing "Toolbars" from the View menu; the XLB file stores these custom settings, including which toolbars are visible, where they are located, and what options are available on each toolbar.
XLB files and allow the same toolbar setup to be transferred from one computer to another or to be used by multiple users. They are typically stored in the [username]\Application Data\Microsoft\Excel folder.
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