Having the right tool for the job doesn't always mean having a different tool for each job. Some tools do double and triple duty. For instance I have a handy little tool that allows me to remove and install glow plugs, tighten ball joints, remove or install tires, and also comes in handy when I need to adjust my slipper clutch on my electric and nitro RCs. It's called a glow plug cross wrench but it's really a super multi-use wrench.
1. Glow plug
As the name suggests, the glow plug cross wrench removes and installs glow plugs. The long end of the wrench reaches down into the head of a nitro engine where fingers don't fit and where using the alternative -- needle nose pliers -- can be frustrating. Pliers don't always maintain as good a grip on the glow plug as the wrench does. Additionally, some glow plug wrenches have little holes that hold and store spare glow plugs.
2. Ball joints
Found in multiple locations on an RC, ball joints on an RC come in various sizes. Instead of having a bunch of loose wrenches to sort through you can use a multi-purpose glow plug cross wrench with its different size arms, thus saving frustration and saving space in your RC tool box.
Most Ready-to-Run RCs come with a tiny little multi-purpose cross wrench that does everything that a good glow plug wrench does -- except for fitting on glow plugs. But it can be way too small for fat fingers to grip. Put on and take off the tires on your RC more easily with the larger glow plug cross wrench.
4. Slipper clutch
Adjusting a slipper clutch is another job for the glow plug cross wrench tool. Turn the little nut on the spur gear to loosen or tighten the drivetrain.