Create RadRangeSlider with a Single Thumb

The following example demonstrates how to remove the SelectionStart thumb of the slider.
Rad Range Slider-How To-One Thumb

You have to add the following references:

xmlns:telerikPrimitives ="using:Telerik.UI.Xaml.Controls.Primitives"
xmlns:telerikRrangeSliderPrimitives ="using:Telerik.UI.Xaml.Controls.Primitives.RangeSlider"

Here is the RadRangeSlider setup:

You will have to disable the SelectionMiddleThumb by setting its IsHitTestVisible property to false.

<telerikInput:RadRangeSlider Grid.Row="0" Minimum="0" SelectionStart="0" TickFrequency="10" Width="300">
    <telerikInput:RadRangeSlider.SliderPrimitiveStyle>
        <Style TargetType="telerikPrimitives:RangeSliderPrimitive">
            <Setter Property="SelectionStartThumbStyle">
                <Setter.Value>
                    <Style TargetType="Thumb">
                        <Setter Property="Visibility" Value="Collapsed"/>
                    </Style>
                </Setter.Value>
            </Setter>
            <Setter Property="SelectionMiddleThumbStyle">
                <Setter.Value>
                    <Style TargetType="Thumb">
                        <Setter Property="BorderThickness" Value="0"/>
                        <Setter Property="Background" Value="#FF006AC1"/>
                        <Setter Property="Height" Value="11"/>
                        <Setter Property="IsHitTestVisible" Value="False"/>
                    </Style>
                </Setter.Value>
            </Setter>
        </Style>
    </telerikInput:RadRangeSlider.SliderPrimitiveStyle>
</telerikInput:RadRangeSlider>