It is a new type of tool that has never been seen before, checking for looseness and attaching / detaching a 6 mm wide square nut attached to the connecting part of a truck chain such as the Izumi V chain. About half of the people who use this truck chain may have experienced that the square nut was loose or lost when they noticed it. Check the nuts with a checker just before the race, before going out, and during breaks during the ride. Work by pushing vertically toward the nut, and the knurled handle provides comfortable torque control.
Actually, this tool is a gem that was designed by a car inspector who knows all about NJS standard machines as a prototype, and took care of shape confirmation, trial, and feedback. The checker is used as a gear to handle the car inspection before the busy race. It is also a tool nominated by head mechanics in New Zealand and Denmark as a tool to be used at the Tokyo Olympics