Impact Super Clamp with Ratchet Handle (Black)

The smaller holes on the back of the Super Clamp allow you to connect accessories to the Super Clamp. As an example, when holding multiple backgrounds on an autopole using a Super Clamp, you may connect the Manfrotto 045 Background Triple Hooks for Three Backgrounds (Box of 2), B&H # MA045, or the Impact Background Triple Hooks - Pair (Black), B&H # IMVPDH3W, via hex screws, or you may connect a single background hook such as the Impact ME-122P Single Background Holder Hooks for Super Clamps (2-Pack), B&H # IMME122P, which may be inserted into the hexagonal 5/8" hole on the back of the unit. There may be other accessories that would also work with the attachment points on a Super Clamp, but the ones listed above would be the popular ones and the ones we carry. We do also carry Super Clamp options that have a grip head connected to the Super Clamp, or connects two Super Clamps together.

The M5 threaded holes are 15mm deep.

Yes, this clamp will work with a 5/8" stud.

This has a clamping range of 0.5 to 2.1 ". I find it indispensable for its intended purpose. I don't believe it was designed to be attached to a wall. There are other alternatives designed specifically for that purpose.

Not sure I understand your question, but - there is a 5/8" stud socket that recieves and locks accessories like your magic arm. There is a threaded female fitting that is on the same face as the socket opening that is 1/4-20 and it looks like it could be tapped to 3/8 if you were careful. It might negate any warranty, however.

Trying to place multiple magic arms on one clamp can easily be over the weight limit that it can handle and we do not know of the existing way do to so.

The little brass piece called a stud fits securely into the clamp and is screwed tight. The one that ships with the clamp has a 1/4" thread, the same kind used in camera tripod sockets, but for a bullhead you typically need a 3/8" thread, so you would have to buy a stud with such a thread like the Manfrotto 036-38. You would then be able to mount your ball head onto the clamp. Another option would be to use a 3/8" to 1/4" reducer bushing with the stud included with the clamp. It's not going to be an incredibly robust fit, though, as the ball head base will only be pressing against the stud rather than the greater surface area of a tripod platform. That said, these clamps are generally used with a Manfrotto 244RC Magic Arm which includes a ball head of sorts (although you will need to replace the Manfrotto QR clamp with a Hejnar Photo FM244 clamp is your camera has an Area-Swiss style QR clamp). The Magic Arm gives you a lot more flexibility and clearance with camera placement.

This clamp was useful to me even yesterday clamping a long junior pin. A hard-rubber piece has to be removed for that but it's easy to put back in place. The whole clamp is sturdy and first class. No complaint here.