The 4s and 8s do have the same type of bowl clips... and on my Alpha 4 the clips have a habit of falling off.

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Thorn use the same black plastic clip on the Alpha 8, Beta 5, Beta 2, Beta 79 and Beta 99.

The earlier white plastic clip was used on the Alpha 8 and Alu Beta 79. Plastic is not the best for a clip. Also the Alpha 3 clip was used on other Thorn lanterns with slight changes to it.

That is a good point, Mike. It is all a matter of reducing costs through the use of standard components (in this instance, the clip). I should think they buy in this standard component from an external supplier.

Well that explains why 1980s Thorn lanterns are often found sans bowl. In Blackpool (home of the 100w SON Alpha 8 MK II on the 5/6m column) there are numerous Alpha 8s to be found without bowls and the vast majority that were casually replaced (and there's been a lot) were because the lantern was missing it's bowl. In the early 90s many of the MK IIs had their bowls replaced with the MK III type, making for a strange hybrid which can still be seen today. Some of the MK IIIs have MK II bowls as well, strangely!  

Mike's right in saying it isn't a great material to use - as there is no spring in it. Those who have ever operated the clip on a Holophane QSM will know it's a very tight clip, and that's because there's resistance against the metal - and once pushed past a certain point then the metal springs the clip into the closed position.... you just don't get that with plastic, plus bits can break off (as has happened with my Beta 79 at some point in the past).

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Yes I would have thought they did buy the component from an external supplier.
I know Simplex did that with clips, as i had to source a new clip for one that was lost on a rareish lantern.

It's all to do with cost versus quality. It must have cost Thorn business in the long-term and could explain why manufacturers like Philips, Urbis and WRTL all overtook them in the 90s and 00s as councils were fed up of ordering replacement bowls for cheapo Thorn lanterns!

And if the bowl didn't get lost (or at least the clip) then it'd fill with water and crud. This was split between being due to a failed canopy or because the clip wasn't pressing the bowl tight against the seal.

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Yeah, I've seen one or two filthy brown Alpha 8s knocking about too. Surprisingly, there are still a few in original, good condition!  

The worst quality lantern has got to be the Urbis Ampera. Not only are the lanterns incredibly bulky (at least the Midi and the Maxi version), but the LEDs frequently fail and they fail individually. Not only that, but the lanterns fill with water and the canopies detach themselves from the lantern on several occasions.