DListView_Column:SetWidth
Example
Creates a DListView and populates it with two columns and two items, only one of which can be selected at a time.
The first column width is 15. The second column width is 350.
local Frame = vgui.Create( "DFrame" )
Frame:SetSize( 500, 500 )
Frame:Center()
Frame:MakePopup()
local SimpleList = vgui.Create( "DListView", Frame )
SimpleList:Dock( FILL )
SimpleList:SetMultiSelect( false )
SimpleList:AddColumn( "Column 1" ):SetWidth(15)
SimpleList:AddColumn( "Column 2" ):SetWidth(350)
SimpleList:AddLine( "First", "Column" )
SimpleList:AddLine( "Second", "Column" )
Output: 
Rust
Steamworks
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