They's just weird, that's what they is. I call 'em Chunkies because their chunky-looking mounting caps initially struck me as comical and possibly even too wide to fit in a standard headshell. About the threaded holes, though. Those are actually square black plastic nuts friction-fit into slots in the sides. A good jostle will make some of them fall out; ask me how I know. If you have your Chunky nuts, you're a lucky man.
Jocularity aside, the 'Chunkies' (real name: Dynamic Interface) followed the EDR.9 into the marketplace around 1981, and this series pretty much replaced the metal ovoid ones Gadget was thinking of.
And yes, they made a smothering blizzard of both types. The metal blob kind came in 3 different inductance flavors, so you have to be careful to put a given body with a stylus that was "voiced" for it. The Chunkies are a little easier, with only two, one for the early few high-falutin' ones and one for the rest of us.
Geek note: Even though Empire had already reached a significant milestone with the previous series of metal-bodied carts, namely the claimed 0.2mg ETM (effective [ie, moving] tip mass) of the 2000Z/T and their clones, they didn't go there again until the 800 UFR Chunky and then the svelte-looking series that followed the Chunkies but used their styli, the GT or "Golden Touch" series.
The EDR.9 reached down to 0.3mg, but during the reign of the cartridges that actually
looked chunky, the styli had ETMs no better than 0.6mg, the same as the old 2000 series. The 800 UFR is the single exception. But then the GT series hit. Their styli have gold-coated cantilevers and have a claimed ETM of 0.18mg. The interesting thing is, they were voiced for 700mH bodies, so the cheapest Chunkies can use GT styli-- if you can find them.
The same strategy goes for the 800 UFR. If you can find it.
To put this all in context, Empire's own CD-4 quad carts (4000D family) were 0.4mg. The 1000ZE/X was 0.5mg. A V15 Type III was 0.33mg and a V15VMR was 0.179mg. All figures are those claimed by their manufacturers, of course. The claimed figure for the first-gen ADC XLM was 0.15mg. Figures from different mfrs can't be directly compared without fudge factors, but you can get a general idea.