TYPE D EXTENSIONS Type D extensions are use for applications where the depth of spindle immersion can be observed and can also be used without a link for rapid spindle changes. TYPE S EXTENSIONS are used for applications where the depth of spindle immersion cannot be seen and can also be sued without a link for rapid spindle changes. EXTENSION LINKS Extension links are used frequently with the Thermosel, UL Adapter and Small Sample Adapter to meet an appropriate immersion.