If your Aluminum Type-C Clamp Hub Pro (ST-TCIMHS, ST-TCIMHM) is not being detected, the most common causes are an iMac that does not have a Thunderbolt 3 port, a USB-C cable that is not fully seated, or an accessory plugged into the wrong port. The Aluminum Type-C Clamp Hub Pro connects through your iMac's Thunderbolt 3 port, and its LED stays on whenever the hub is receiving power.

How to fix detection problems with the Aluminum Type-C Clamp Hub Pro

1. Confirm your iMac is supported. The Aluminum Type-C Clamp Hub Pro is designed for the 2017, 2019, and 2020 iMac and the iMac Pro (2017), which have Thunderbolt 3 (USB-C) ports.
2. Rule out the models it does not fit. The Aluminum Type-C Clamp Hub Pro does not fit the 24-inch M1 (2021) iMac because of the updated design, and it does not fit the Studio Display. Pre-2017 iMacs use Thunderbolt 2, which is not the same as Thunderbolt 3.
3. If you have a 2016 or older iMac, connect the Aluminum Type-C Clamp Hub Pro to an open USB-A port using a Type-A to Type-C adapter, sold separately.
4. Plug the hub's USB-C cable firmly into your iMac's Thunderbolt 3 port, then check the LED on the Aluminum Type-C Clamp Hub Pro. The LED cannot be switched off, so a dark LED means the hub is not receiving power.
5. Try the other Thunderbolt 3 port on your iMac.
6. Unplug the Aluminum Type-C Clamp Hub Pro, wait a few seconds, then reconnect it.
7. Restart your iMac fully, then reconnect the Aluminum Type-C Clamp Hub Pro and test again.
8. Check the clamp mount. Turn the knob until the clamps are hidden inside the case, insert the Aluminum Type-C Clamp Hub Pro into the air vents on the bottom of your iMac, then turn the knob the opposite direction and confirm the hub is fastened securely.
9. Match your accessory to the right port. The USB-C port on the Aluminum Type-C Clamp Hub Pro is a data-only port running at USB 3.0 speeds up to 5 Gbps with 2.5W of output, so it does not support video output or charging. Use it for flash drives, smaller external hard drives, and peripherals like a mouse or keyboard, not for charging an iPad or an iPhone.
10. Use the USB-A data ports for standard USB devices. They do not support CD readers, including the Apple SuperDrive, because of the power those drives require.
11. For a memory card that does not appear, push the card fully into the slot, then check Disk Utility to see whether it shows up. The SD and microSD readers recognize UHS-II cards but operate at UHS-I speeds.
12. Test the Aluminum Type-C Clamp Hub Pro on another USB-C computer. The clamp only mounts to an iMac, but the ports still work when connected to another Mac, which tells you whether the hub itself is working.

If the problem continues after these steps, submit a support request.