Hi Basil:
In answer to your questions my reply is...
In self defense, and quite well!
Let me explain...During a restoration project of an old Volvo I found that air filters for the SU carburetors were no longer available at any local parts stores.
Nor were there any good alternatives on the internet (these SUs are the "three bolt" H6 type). Even the paper element types were far too expensive as throw aways.
The upshot of this was...I designed and built my own. The features I wanted were: 1. easily servicable/reusable elements, 2.include an internal airhorn, 3. must look good and last, but not least 4. would only require me to contort/drop/swear once to install the back nuts!
Since I am in the manufacturing industry I have the equipment and experience to set this sort of thing up, and in fact used a previous design for encoder end plates to fixture the filter plates. I also researched and found the best price/performance filter element (IMHO) on the market. The two stage foam "sock" made by UNI filters, with an additional internal support.
Since, in the world of CNC machining, "only the first one is hard" is proverbial, I decided to build a few and offer them to others.
Whether this will be worth the trouble time and expense, or is even a good idea, I don't yet know.
No doubt the market will give me an answer in short order!
Cheers!
Dave G.
https://su-filters.com