What did cable installer use to tap onto my service ground?

Question

I have a somewhat mysterious service ground apparently underneath a concrete entryway. All that is visible now is a heavy gauge bare copper wire coming through the cement. When the cable company hooked up my internet they bonded the coax ground to this service ground using some sort of clamp:

What is this square clamp called? I have pored through hundreds of Google Images for "ground clamp" and "square ground clamp" and "copper ground lug" and whatever else I can think of and am not finding something like this, which is apparently designed for bonding in this sort of situation.

I am adding some of my own antennas and need to bond their grounds to this same service ground wire. So I need something like this that can split into two pieces around the middle of my service ground wire, and clamp it tightly onto the end of an additional ground wire.

(Rather than directly connecting my lightning arrestors, in actuality I'll probably be driving a second "known quantity" ground rod nearby, and bonding that to the service ground — but then I'll still need basically the same sort of clamp.)

Answer 1

This looks to be a type of connector called a "split bolt". They are a pain to insulate, so they're most commonly used for grounding, but when wrapped thoroughly in insulating tape they can be used for connecting live wires. They're most commonly seen on heavy gauge wires where wire nuts are no longer an option, or when tapping conductors as you see here.

A more common variation on the split bolt is shown below.

Answer 2

Thanks to the "split" term in ThreePhaseEel's answer, I finally chanced upon a close match via an image search. Apparently these are called "vise connectors".

For example, GMP Tools calls theirs a "Ground Vise Connector" (part number 77966) and MacLean Power Systems sells a "Bronze Vise Connector" under a variety of variants (e.g. catalog numbers BVC-2/4/6 depending on size). Allied Bolt calls them a "Bronze Vise Compression Connector" (e.g. part number 862), and also offers something very similar they call an "H Connector".

I'm not sure how they compare to the split bolt. I suspect they're a little handier for cable techs since the halves don't need to be fully separated to install, and/or are better for bonding two different gages of wire. In my case, it looks like the local home improvement stores tend to carry the split bolts and not these vise connectors.