I ordered the Twin Tech barrel kit, which comes with a threaded endcap (for when the adapter isn't installed) and adapter for 1/2x28 threads, but did not include a thread protector for the adapter (IMO, they should have supplied this as part of the kit, they charged enough for it).
The installation was easy, took less than 2 minutes. Everything dropped right in w/o any hassles and fits perfectly, no rubs or clearance issues. My Sparrow threads right up and the centerline clearance is perfect, little or no chance of a baffle or end cap strike as far as I can see. I am planning on running a few rounds through it this weekend to check for function and accuracy (if this 100+ degree weather will let up, some, it's been brutally hot here for the last week, 4 new all-time records in 6 days!).
I'll post an AA report here if I can get out for the testing I have planned.
I do not work for Twin Tech, nor do I have any interest in the company, save that they got there first with the threaded barrels that Ruger should have installed at the factory from the get-go.
IMO, another HUGE blunder on Ruger's part. Now, they're losing money because of it.