This can be done by exposing a spacing property for the particular Series. 

For the time being mentioned properties can be set on the client through the chartObject of the RadHtmlChart:
JavaScript:
	<telerik:RadCodeBlock ID="RadCodeBlock1" runat="server">
		<script type="text/javascript">
			function ChangeSpace() {
				var chart = $find("<%=ColumnChart.ClientID%>");
				chart._chartObject.options.series[0].spacing = 0.9;
				chart.repaint();
			}

			function ChangeGap() {
				var chart = $find("<%=ColumnChart.ClientID%>");
				chart._chartObject.options.series[0].gap = 10;
				chart.repaint();
			}
		</script>
	</telerik:RadCodeBlock>
ASPX:
		<telerik:RadButton ID="RadButton1" runat="server" AutoPostBack="false" Text="Change Space" OnClientClicked="ChangeSpace" />
		<telerik:RadButton ID="RadButton2" runat="server" AutoPostBack="false" Text="Change Gap" OnClientClicked="ChangeGap" />
		<telerik:RadHtmlChart runat="server" ID="ColumnChart" Transitions="true">
....
		</telerik:RadHtmlChart>

When data-bound categorical series has zeros in the x-axis labels they are parsed and the zeros disappear. For example:
ASPX:

            <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
            <telerik:RadHtmlChart runat="server" ID="Radhtmlchart1">
                <PlotArea>
                    <Series>
                        <telerik:ColumnSeries DataFieldY="Score1"></telerik:ColumnSeries>
                   </Series>

                   <XAxis DataLabelsField="Student">
                    </XAxis>
                </PlotArea>
            </telerik:RadHtmlChart>

C#:

    protected void Page_Load(object sender, EventArgs e)
    {
        Radhtmlchart1.DataSource = GetData();
        Radhtmlchart1.DataBind();
    }
    protected DataTable GetData()
    {
        DataTable table = new DataTable();

        table.Columns.Add("Student", typeof(string));
        table.Columns.Add("Score1", typeof(int));

        table.Rows.Add(new object[] { "0806014562", 40 });
        table.Rows.Add(new object[] { "0806014562", 50 });
        table.Rows.Add(new object[] { "0806014562", 70 });
        return table;
    }
Workarounds:
1) Use format string to add the desired missing zeros when parsed.

<LabelsAppearance DataFormatString="0{0}"></LabelsAppearance>

2) Add items programmatically

    protected void Page_Load(object sender, EventArgs e)
    {
        Radhtmlchart1.DataSource = GetData();
        Radhtmlchart1.DataBind();

        DataTable currDT = GetData();
        for (int i = 0; i < currDT.Rows.Count; i++)
        {
            AxisItem currItem = new AxisItem(currDT.Rows[i]["Student"].ToString());
            Radhtmlchart1.PlotArea.XAxis.Items.Add(currItem);
        }
    }

When Series are created programmatically, Axes settings are not preserved after postback. The workaround is to create an empty series in the markup. For example:

        <telerik:RadHtmlChart ID="RadHtmlChart1" runat="server">
...
            <PlotArea>
                <YAxis>...</YAxis>
                <XAxis>...</XAxis>
                <Series>
                    <telerik:ScatterLineSeries Name=" ">
                        <Appearance FillStyle-BackgroundColor="Transparent"></Appearance>
                    </telerik:ScatterLineSeries>
                </Series>
            </PlotArea>
        </telerik:RadHtmlChart>

Series tooltips are not visible in a Stock chart when the same series is added programmatically in the plotarea and the navigator simultaneously.

The workaround is to:
1) Create different series for the plot area and the navigator.
2) Explicitly set the tooltips' visibility with JS like this:
        <script type="text/javascript">
            function pageLoad() {
                var chart = $find("Chart");
                var series = chart._chartObject.options.series[0];
                series.tooltip.visible = true;
                //repaint the chart to apply the changes
                chart.repaint();
            }
        </script>

For the time being you can set the property through the kendoWidget. All available options are available at http://docs.telerik.com/kendo-ui/api/javascript/dataviz/ui/chart#configuration-series.connectors
        <script>
            function pageLoad() {
                var kendoWidget = $find("<%=RadHtmlChart1.ClientID%>")._chartObject;
                kendoWidget.options.series[0].connectors = {width: "3", color: "#ff0000"};
                kendoWidget.redraw();
            }
        </script>
        <telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" Width="400px" Height="400px">
            <PlotArea>
                <Series>
                    <telerik:PieSeries>
                        <SeriesItems>
                            <telerik:PieSeriesItem Y="30" />
                            <telerik:PieSeriesItem Y="10" />
                            <telerik:PieSeriesItem Y="20" />
                        </SeriesItems>
                    </telerik:PieSeries>
                </Series>
            </PlotArea>
        </telerik:RadHtmlChart>

When using the RadHtmlChart RadarSeries the axis are default drawn like a spiders web. (see screenshot)

A common request is that axis lines for this type of graph are drawn as circles (represending more a Radar type look).

This can currently be achieved by accessing the Kendo widget like so:

$find('RadarAreaChart').get_kendoWidget().options.valueAxis.majorGridLines.type="arc";
$find('RadarAreaChart').get_kendoWidget().options.valueAxis.minorGridLines.type="arc";
$find('RadarAreaChart').get_kendoWidget().redraw();

But it would be VERY convenient (and probably very easy to implement for you guys :-) if it was a setting on the RadarSeries itself (or perhaps on the axis of the RadarSeries.

E.g. property on RadarSeries called AxisType with values (Spider or Radar).

Best Regards

Thomas

The property (http://docs.telerik.com/kendo-ui/api/javascript/dataviz/ui/chart#configuration-categoryAxis.maxDateGroups) can be set through the kendoWidget:
JavaScript:

        <script>
            function OnLoad(args) {
                var kendoWidget = args.get_kendoWidget();
                kendoWidget.options.categoryAxis.maxDateGroups = 8;
                kendoWidget.options.categoryAxis.baseUnit = 'fit';
                kendoWidget.redraw();
            }
        </script>

ASPX:

        <telerik:RadHtmlChart runat="server" ID="RadHtmlChart2" Width="640px" Height="480px">
            <ClientEvents OnLoad="OnLoad" />
            <PlotArea>
                <Series>
                    <telerik:LineSeries DataFieldY="SellQuantity">
                        <LabelsAppearance DataFormatString="{1} cars sold on {0:m}">
                        </LabelsAppearance>
                        <TooltipsAppearance Color="White" DataFormatString="{1} cars sold on<br/>{0:D}" />
                    </telerik:LineSeries>
                </Series>
                <XAxis DataLabelsField="SellDate">
                    <TitleAppearance Text="Sell Date">
                    </TitleAppearance>
                    <LabelsAppearance DataFormatString="d">
                    </LabelsAppearance>
                    <MajorGridLines Color="#EFEFEF" Width="1"></MajorGridLines>
                    <MinorGridLines Color="#F7F7F7" Width="1"></MinorGridLines>
                </XAxis>
                <YAxis>
                    <TitleAppearance Text="Quantity">
                    </TitleAppearance>
                    <MajorGridLines Color="#EFEFEF" Width="1"></MajorGridLines>
                    <MinorGridLines Color="#F7F7F7" Width="1"></MinorGridLines>
                </YAxis>
            </PlotArea>
            <ChartTitle Text="Sold Cars per Date">
            </ChartTitle>
        </telerik:RadHtmlChart>

C#:

    protected void Page_Load(object sender, EventArgs e)
    {
        RadHtmlChart2.DataSource = GetData();
        RadHtmlChart2.DataBind();
    }

    protected DataTable GetData()
    {
        DataTable dt = new DataTable();

        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("SellQuantity", typeof(int));
        dt.Columns.Add("SellDate", typeof(DateTime));

        dt.Rows.Add(1, 2, new DateTime(2011, 06, 12));
        dt.Rows.Add(2, 5, new DateTime(2011, 12, 12));
        dt.Rows.Add(3, 6, new DateTime(2012, 06, 17));
        dt.Rows.Add(4, 4, new DateTime(2012, 09, 18));
        dt.Rows.Add(5, 7, new DateTime(2013, 03, 18));

        return dt;
    }

Currently BarSeries/ColumnSeries are rendered like a "glass" gradient and PieSeries/DonutSeries like a "roundedBevel" gradient. Expose an OverlayGradient property that lets you control the gradient (e.g. "glass", "roundedBevel", "sharpBevel", "none"). For the time being the properties can be set through the chartObject:
JavaScript:
	<telerik:RadCodeBlock ID="RadCodeBlock1" runat="server">
		<script>
			function pageLoad() {
				var chart1 = $find("<%=ColumnChart1.ClientID%>");
				//Set glass gradient to first series
				chart1._chartObject.options.series[0].overlay = { gradient: "glass" };
				//Remove gradient from second series
				chart1._chartObject.options.series[1].overlay = { gradient: "none" };
				chart1.repaint();

				var chart2 = $find("<%=PieChart1.ClientID%>");
				//Set sharpBevel gradient to pie series
				chart2._chartObject.options.series[0].overlay = { gradient: "sharpBevel" };
				chart2.repaint();
			}
		</script>
	</telerik:RadCodeBlock>
ASPX:
		<telerik:RadHtmlChart runat="server" ID="ColumnChart1" Transitions="true">
			<PlotArea>
				<Series>
					<telerik:ColumnSeries Name="Series with Gradient">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="15000" />
							<telerik:CategorySeriesItem Y="23000" />
							<telerik:CategorySeriesItem Y="10000" />
							<telerik:CategorySeriesItem Y="16000" />
						</SeriesItems>
					</telerik:ColumnSeries>
					<telerik:ColumnSeries Name="Series with no Gradient">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="35000" />
							<telerik:CategorySeriesItem Y="10000" />
							<telerik:CategorySeriesItem Y="20000" />
							<telerik:CategorySeriesItem Y="17000" />
						</SeriesItems>
					</telerik:ColumnSeries>
				</Series>
			</PlotArea>
		</telerik:RadHtmlChart>
		<telerik:RadHtmlChart runat="server" ID="PieChart1" Transitions="true" Width="450px" Height="450px">
			<PlotArea>
				<Series>
					<telerik:PieSeries StartAngle="90">
						<SeriesItems>
							<telerik:PieSeriesItem BackgroundColor="Purple" Exploded="true" Name="Internet Explorer" Y="18.3" />
							<telerik:PieSeriesItem BackgroundColor="Orange" Exploded="false" Name="Firefox" Y="35.8" />
							<telerik:PieSeriesItem BackgroundColor="Green" Exploded="false" Name="Chrome" Y="38.3" />
							<telerik:PieSeriesItem BackgroundColor="Blue" Exploded="false" Name="Safari" Y="4.5" />
							<telerik:PieSeriesItem BackgroundColor="Red" Exploded="false" Name="Opera" Y="2.3" />
						</SeriesItems>
					</telerik:PieSeries>
				</Series>
			</PlotArea>
			<ChartTitle Text="Pie with Gradient">
			</ChartTitle>
		</telerik:RadHtmlChart>

The property will be like similar to http://docs.telerik.com/kendo-ui/api/dataviz/chart#configuration-categoryAxis.autoBaseUnitSteps.
For the time being the property can be set through the kendo widget:
ASPX:
		<script type="text/javascript">
			function pageLoad() {
				var kendoWidget = $find("<%=RadHtmlChart1.ClientID%>").get_kendoWidget();
				kendoWidget.options.categoryAxis.baseUnitStep = "auto";
				kendoWidget.options.categoryAxis.autoBaseUnitSteps = { months: [4] };
				kendoWidget.redraw();
			}
		</script>
		<telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" Width="600" Height="400">
			<PlotArea>
				<Series>
					<telerik:ColumnSeries DataFieldY="SellQuantity">
					</telerik:ColumnSeries>
				</Series>
				<XAxis DataLabelsField="SellDate" >
					<LabelsAppearance DataFormatString="MM/yyyy" RotationAngle="45"></LabelsAppearance>
				</XAxis>
			</PlotArea>
		</telerik:RadHtmlChart>
C#:
	protected void Page_Load(object sender, EventArgs e)
	{
		RadHtmlChart1.DataSource = GetData();
		RadHtmlChart1.DataBind();
	}

	protected DataTable GetData()
	{
		DataTable dt = new DataTable();

		dt.Columns.Add("ID", typeof(int));
		dt.Columns.Add("SellQuantity", typeof(int));
		dt.Columns.Add("SellDate", typeof(DateTime));

		dt.Rows.Add(1, 2, new DateTime(2011, 01, 01));
		dt.Rows.Add(1, 2, new DateTime(2011, 06, 01));
		dt.Rows.Add(2, 5, new DateTime(2011, 12, 01));
		dt.Rows.Add(3, 6, new DateTime(2012, 06, 01));
		dt.Rows.Add(4, 4, new DateTime(2012, 09, 01));
		dt.Rows.Add(5, 7, new DateTime(2013, 03, 01));

		return dt;
	}

For the time being you can use the following workaround:
1) Either hide the chart with visibility:hidden instead of display:none
2) Or use the following workaround:
		<div id="div1" style="display: none;">
			<telerik:RadHtmlChart runat="server" ID="ColumnChart1" Width="600px" Height="400px">
				<PlotArea>
					<Series>
						<telerik:ColumnSeries Name="Product 1">
							<SeriesItems>
								<telerik:CategorySeriesItem Y="1" />
								<telerik:CategorySeriesItem Y="2" />
								<telerik:CategorySeriesItem Y="3" />
							</SeriesItems>
						</telerik:ColumnSeries>
					</Series>
				</PlotArea>
			</telerik:RadHtmlChart>
		</div>
		<input type="button" onclick="showChart(); return false;" value="Show Chart" />
		<script>
			Telerik.Web.UI.RadHtmlChart.prototype._getMainConfig = function () {
				var that = this;
				//when visible is false - nothing is sent from the server to save transferred data
				//e.g - there are properties set but visible is false - we do not need to send those properties amyway
				//that is why - set visible: false when nothing is sent from the server
				that._options = $telerik._getPropertiesParameter(that, that.constructor);
				that._cleanUpConfigProperties();

				that._options["theme"] = that.get_skin();
				//that._options["visible"] = $(that.get_element()).is(':visible');
				that._options["title"] = that._chartTitle ? that._parseObject(that._chartTitle) : { visible: false };
				that._options["legend"] = that._legend ? that._parseObject(that._legend) : { visible: false };

				if (that._chartArea) {
					that._options["chartArea"] = that._parseObject(that._chartArea);
				}

				if (that._isSparklineChart()) {
					that._setMinimumSparklineWidth();
				}

				if (that._plotArea) {
					that._configurePlotArea();
				}

				if (that._series) {
					/*jshint evil: true */
					that._options["series"] = eval(that._series);
					/*jshint evil: false */
				}

				if (that._isStockChart()) {
					that._configureStockChart();
				}
			}
		</script>

String data source fields in the RadHtmlChart that contain only numeric characters should not be parsed to decimal. Also when such a string starts with the 0 character, it is omitted. For example the "0" item in the legend is not displayed with the example below:
ASPX:

        <telerik:RadHtmlChart runat="server" ID="PieChart1" Width="800" Height="500" Transitions="true">
            <Appearance>
                <FillStyle BackgroundColor="White"></FillStyle>
            </Appearance>
            <ChartTitle Text="Browser Usage for April 2012">
                <Appearance Align="Center" BackgroundColor="White" Position="Top">
                </Appearance>
            </ChartTitle>
            <Legend>
                <Appearance BackgroundColor="White" Position="Right" Visible="true">
                </Appearance>
            </Legend>
            <PlotArea>
                <Appearance>
                    <FillStyle BackgroundColor="White"></FillStyle>
                </Appearance>
                <Series>
                    <telerik:PieSeries StartAngle="90" DataFieldY="code_count" NameField="items_names">
                        <LabelsAppearance Position="OutsideEnd" DataFormatString="{0} %">
                        </LabelsAppearance>
                        <TooltipsAppearance Color="White" DataFormatString="{0} %"></TooltipsAppearance>
                    </telerik:PieSeries>
                </Series>
            </PlotArea>
        </telerik:RadHtmlChart>

C#:

using System.Data;

    protected void Page_Load(object sender, EventArgs e)
    {
        PieChart1.DataSource = GetData();
        PieChart1.DataBind();
    }

    protected DataTable GetData()
    {
        DataTable dt = new DataTable();

        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("code_count", typeof(int));
        dt.Columns.Add("items_names", typeof(string));

        dt.Rows.Add(1, 771, "0");
        dt.Rows.Add(2, 187, "1");
        dt.Rows.Add(3, 178, "2");
        dt.Rows.Add(4, 60, "3");

        return dt;
    }

Currently the datasource columns which have space in their name cannot be passed to a databound RadHtmlChart. Add the ability to handle the spaces in the names of these columns.