>>10344109If you mean the part at the blue line, it's just an overspray protector and is usually not, strictly speaking, critical. If you're doing a fine detail spray it might be more useful to be able to see the needle for precision.
If you mean the part at the red line, I have no idea if it would work or not since it's not something I've ever had come up or seen come up since I've had no reason to try and operate an airbrush without it.
