This is an RPM Toe-In Gauge and is intended for use with 1/10 and 1/8 on and off-road vehicles. If you are a hobbyist that enjoys R/C vehicles or an all-out R/C racer or anywhere in between, this tool is a must for your toolbox! This toe-in gauge allows you to do trackside checks of the toe angles without removing the wheels! This gauge checks toe through the simple method of comparing the width of the wheels at the rear of the tire to the width of the wheels at the front of the tire! This gauge is accurate to within one-half of a degree per side and closer, and can also be used to check the legal width of off-road buggies and trucks. The gauge comes with a second thumbscrew hole to check narrower vehicles such as sedans as well.