1- First, if your rotary tool has a threaded collar on the motor end, you will need to remove it by turning CCW (counter clockwise). You will need the collar when you attach a tool directly to the rotary tool. You will not need it with the flex shaft.
2- Hold the flexible shaft by the silver color fitting end (you will be able to see the inner shaft core). And pull the inner core about 2 inches. If you need a pair of pliers to hold it, that’s normal.
It is a very good idea to grease (lube) the inner core.
MAKE SURE THE ROTARY TOOL IS UNPLUGGED FOR THE NEXT STEPS
3-Now, the idea is you are attaching the core of the flex shaft into the rotary tool collet just like you would attach any kind of tool with a 1/8″ shaft. The flex shaft is there to transfer the rotation, that’s it. It is just like an extension. Push the core of the flex shaft into the rotary tool collet and tighten the collet. You can use the collet lock button to prevent it from turning while you are tightening the nut.
4- You can now screw the silver color fitting end of the flex shaft onto the rotary tool housing. This is where you removed the collar. We are now done attaching the flex shaft to the rotary tool. From now on, the next steps are about attaching the bit or burr to the flex shaft.
5- The other end (BLACK COLOR) of the flex shaft is where you will insert the desired attachment tool such as a diamond disc or a burr. You will be using the silver chrome L shaped piece for this stage. There is a hole on the side of the black side of the flex shaft. And there is another hole under the black side. When you align these two holes by turning the silver tip on the black end, insert the L shaped metal. This step may sound confusing but it’s simple. The inner metal part on the black end of the shaft will want to turn as you try to attach the tool. The L shaped metal is there to help you hold it while you try to twist the tip.
6- You can now attach the bit. And tighten the nut at the tip of the black end of the flex shaft.