property Items.CellHasRadioButton([Item as Variant], [ColIndex as Variant]) as Boolean

Retrieves or sets a value indicating whether the cell has associated a radio button or not.

TypeDescription
Item as Variant A long expression that indicates the item's handle.
ColIndex as Variant A long expression that indicates the column's index, a string expression that indicates the column's caption or the column's key.
Boolean A boolean expression that indicates whether the cell contains a radio button.

Retrieves or sets a value indicating whether the cell has associated a radio button or not. To change the state for a radio cell you have to use CellState property. The cell cannot display in the same time a radio and a check button. The control fires CellStateChanged event when the cell's state has been changed. To set the cell of check type you have call CellHasCheckBox  property.  To add or remove a cell to a given radio group you have to use CellRadioGroup property. The following sample shows how to set the radio type for all cells of the first column, and group all of them in the same radio group ( 1234 ): 

Dim h As Variant
With ExplorerTree1.Groups(0)
    .BeginUpdate
    With .Items
        For Each h In ExplorerTree1.Groups(0).Items
            .CellHasRadioButton(h, 0) = True
            .CellRadioGroup(h, 0) = 1234
        Next
    End With
    .EndUpdate
End With

or

Private Sub ExplorerTree1_AddItem(ByVal Group As EXPLORERTREELibCtl.IGroup, ByVal Item As EXPLORERTREELibCtl.HITEM)
    With Group.Items
        .CellHasRadioButton(Item, 0) = True
        .CellRadioGroup(Item, 0) = 1234
    End With
End Sub

To find out the radio cell that is checked in the radio group 1234 you have to call: MsgBox Group.Items.CellCaption(, Group.Items.CellChecked(1234)) 

The following sample group all cells of the first column into a radio group, and display the cell's checked on the radio group when the state of a radio group has been changed:

Private Sub ExplorerTree1_AddItem(ByVal Group As EXPLORERTREELibCtl.IGroup, ByVal Item As EXPLORERTREELibCtl.HITEM)
    With Group.Items
        .CellHasRadioButton(Item, 0) = True
        .CellRadioGroup(Item, 0) = 1234
    End With
End Sub

Private Sub ExplorerTree1_CellStateChanged(ByVal Group As EXPLORERTREELibCtl.IGroup, ByVal Item As EXPLORERTREELibCtl.HITEM, ByVal ColIndex As Long)
    Debug.Print "In the 1234 radio group the """ & Group.Items.CellCaption(, Group.Items.CellChecked(1234)) & """ is checked."
End Sub

Note: A cell is the intersection of an item with a column. All properties that has an Item and a ColIndex parameters are referring to a cell. The Item parameter represents the handle of an item, and the ColIndex parameter indicates an index ( a numerical value, see Column.Index property ) of a column , the column's caption ( a string value, see Column.Caption property ), or a handle to a cell. Here's few hints how to use properties with Item and ColIndex parameters:

Group.Items.CellBold(, Group.Items.ItemCell(Group.Items(0), 0)) = True
Group.Items.CellBold(Group.Items(0), 0) = True
Group.Items.CellBold(Group.Items(0), "ColumnName") = True