Heat Stippling
Heat stippling is a technique done with a wood burner, which is essentially the same design as a soldering iron. With a pointed tip, super-heated by electricity, the tip is lightly applied -- usually to plastic -- to create a texture. Rows of stippled indentations can create a texture not unlike the checkering found on wood firearm grips. In fact, heat stippling is often used on firearm grips.
Soldering Iron and Custom Wood Burners
Older soldering iron designs were longer, providing space between the hot tip and the handle to keep you from burning yourself. The space is an effective safety measure, but doesn't lend itself to detail work. Ideally, you want to hold your soldering iron or wood burner like a pen or pencil, with your fingertips, giving you the dexterity for fine control. Newer wood burner designs often have ergonomics that better lend themselves to heat stippling. They also tend to have a heat-guard to protect your fingertips from burns.
Single Tips
Most newer wood burners -- and many older wood burners or soldering irons -- have at least a handful of interchangeable tips. Not all tips are well-suited for heat stippling. While any tip is capable of burning a texture into a plastic hand-grip, it may not be a desirable pattern. A common stippling tip is simply a rounded tip nearly identical in shape to a fine ballpoint pen. Dots are then made in tight rows, one next to another, created a solid field of round heat-stippled indentations.
Patterned Tips
Another option is a tip that doesn't make a single stipple mark, but multiple marks, or a more complex indentation, similar to a waffle iron. Custom wood-burning kits are much more likely to include an array of tip designs. They may improve the aesthetics or they may simply make your job go faster. If you don't find the tip you want, you can customize your own tip with hand files as they are commonly brass and relatively easy to shape.