Quartet: Is the long thumb screw on the back an earth ground connection? Chris February 23, 2021 21:23 Updated Answer: No ,The thumb screw on the back panel is designed to be used as a cable clamp, it is used to secure the USB, and or the AC power cables in a loop so they are not easily disconnected. Related articles Quartet doesn't power up and is not recognized after waking the Mac from sleep Can the brightness of Quartet's Touchpads or OLED screens be adjusted? Do my settings get stored on the Mac or in Quartet? Power Supply Information: Element / Quartet / Thunderbridge Can I use balanced TRS cables to connect line-level devices such as external mic pres? Comments 0 comments Article is closed for comments.