Use the CellRadioGroup property to add or remove a radio button from a group. In a radio group only one radio button can be checked. A radio cell cannot be contained by two different radio groups. Use the CellHasRadioButton property to add a radio button to a cell. When the cell's state is changed the control fires the CellStateChanged event. The CellState property specifies the cell's state. By default, when a cell of radio type is created  the radio cell is not grouped to any of existent radio groups 

The following VB sample sets the radio type for all cells in the first column, and group all of them in the same radio group ( 1234 ):

Dim h As Variant
Grid1.BeginUpdate
With Grid1.Items
For Each h In Grid1.Items
    .CellHasRadioButton(h, 0) = True
    .CellRadioGroup(h, 0) = 1234
Next
End With
Grid1.EndUpdate

or

Private Sub Grid1_AddItem(ByVal Item As EXGRIDLibCtl.HITEM)
    Grid1.Items.CellHasRadioButton(Item, 0) = True
    Grid1.Items.CellRadioGroup(Item, 0) = 1234
End Sub

To find out the radio cell that is checked in the radio group 1234 you can use: MsgBox Grid1.Items.CellValue(, Grid1.Items.CellChecked(1234))

The following sample groups all cells of the first column into a radio group, and displays the checked cell:

Private Sub Grid1_AddItem(ByVal Item As EXGRIDLibCtl.HITEM)
    Grid1.Items.CellHasRadioButton(Item, 0) = True
    Grid1.Items.CellRadioGroup(Item, 0) = 1234 ' The 1234 is arbirary and it represents the identifier for the radio group
End Sub

Private Sub Grid1_CellStateChanged(ByVal Item As EXGRIDLibCtl.HITEM, ByVal ColIndex As Long)
    Debug.Print "In the 1234 radio group the """ & Grid1.Items.CellValue(, Grid1.Items.CellChecked(1234)) & """ is checked."
End Sub

The following VB sample assigns a radio button to the focused cell:

With Grid1.Items
    .CellHasRadioButton(.FocusItem, Grid1.FocusColumnIndex) = True
    .CellRadioGroup(.FocusItem, Grid1.FocusColumnIndex) = 1234
End With

The following C++ sample assigns a radio button to the focused cell:

#include "Items.h"
CItems items = m_grid.GetItems();
COleVariant vtItem(items.GetFocusItem()), vtColumn( m_grid.GetFocusColumnIndex() );
items.SetCellHasRadioButton( vtItem, vtColumn, TRUE );
items.SetCellRadioGroup( vtItem, vtColumn, 1234 );

The following VB.NET sample assigns a radio button to the focused cell:

With AxGrid1.Items
    .CellHasRadioButton(.FocusItem, AxGrid1.FocusColumnIndex) = True
    .CellRadioGroup(.FocusItem, AxGrid1.FocusColumnIndex) = 1234
End With

The following C# sample assigns a radio button to the focused cell:

axGrid1.Items.set_CellHasRadioButton(axGrid1.Items.FocusItem, axGrid1.FocusColumnIndex, true);
axGrid1.Items.set_CellRadioGroup(axGrid1.Items.FocusItem, axGrid1.FocusColumnIndex, 1234);

The following VFP sample assigns a radio button to the focused cell:

with thisform.Grid1.Items
	.DefaultItem = .FocusItem
	.CellHasRadioButton(0,thisform.Grid1.FocusColumnIndex) = .t.
	.CellRadioGroup(0,thisform.Grid1.FocusColumnIndex) = 1234
endwith

Note: The intersection of an item with a column defines a cell. Each cell is uniquely represented by its handle. The cell's handle is of HCELL type, that's equivalent with a long type. All properties of Items object that have two parameters Item and ColIndex, refer a cell.

The following lines are equivalents and each of them changes the bold font attribute of the first cell on the first item.

With Grid1
    .Items.CellBold(, .Items.ItemCell(.Items(0), 0)) = True
    .Items.CellBold(.Items(0), 0) = True
    .Items.CellBold(.Items(0)) = True
    .Items.CellBold(.Items.ItemByIndex(0)) = True
    .Items.CellBold(.Items.ItemByIndex(0), 0) = True
    .Items.CellBold(.Items(0), Grid1.Columns(0).Caption) = True
End With