Question Purpose of the spark plug sleeve in a CubCrafters Lycoming 363i engine?

[Neal]

The 363i is a custom and experimental engine CubCrafters modified from a Lycoming IO-360 to lighten it and take it to 186 HP. In my recent condition inspection I questioned where the 15 ft-lb torque setting came from for the spark plugs as they come out easily when torqued at 15 ft-lbs, too easily? I ended up finding that info in this post but in a discussion with fellow FX-3 owner @Tsquared he had a note from his A&P he uses for condition inspections regarding different torque values and diameters of plugs including a sleeve torque. Sleeve? What are you talking about I asked...did my A&P last year discard something during the condition inspection done at Raleigh at a CubCrafters "service center"??? Now I'm worried I may have done something terrible, long story short, no, if you didn't have said sleeve the spark plug would not have anything to thread into.

When I got my compression tester the fittings were too large and I learned that my plugs are automotive size plugs, 14mm, vs the much larger size my tester was configured for. I ordered the correct adapter which came yesterday and I completed the compression tests. I took a picture of this "sleeve" and wonder WHY? Why is this in the engine? Is this just so we can use automotive size spark plugs? Without this sleeve would we need the larger and more expensive plugs? And of course there are maintenance considerations needed for this sleeve, and related components.

Anyone know the purpose of this or backstory?