Used to be when soldering the lead of a heat-sensitive component, you were supposed to clip on a heat sink to dissipate the heat away from the component. But with surface-mount components replacing through-hole components, the heat sink has been slowly moving to the back of the toolbox where tools go to retire. The tool hasn’t become obsolete yet, though — you can still find plenty of heat-sensitive specialty and hobbyist parts with leads.
This version from Miller is an example of a quality heat sink. The spring-loaded copper jaws efficiently absorb heat and move it away from the sensitive component, while the nickel plating ensures that solder won’t stick to the tool. To stop the heat from being efficiently transferred to your hand when you remove the heat sink, Miller coats the handles in soft plastic.
Unfortunately, I can’t find the Miller tool for sale, but for comparison I included links to inexpensive Radio Shack and Hexacon heat sinks that’ll probably get the job done for $2 to $7.