The documented job is “How to Cut In and Roll Behind Radiators, Toilets, and Appliances”.
✕DO NOT FORCE THE FIT
Open walls and ceilings — 4 inches is a cavity-and-panel width, and the long frame doesn't change that.
Fine gloss finishing on visible cabinet doors — the 15/32″ pile leaves more stipple than a gloss cabinet face wants, and the long frame fights precise control; that's a 1/4″ or foam mini's job.
Rough masonry — the woven pile is short and its fine fibers snag on aggregate.
And it isn't a substitute for moving the obstacle when you can: where a fixture can be pulled fully clear, a normal roller gives a better finish than reaching past it — the long frame is for what you can't move.
into blind cavities, err light — an overloaded cover drips where you can't blot it, and 15/32″ carries enough to drip. Mind the leverage: a 16-inch frame multiplies any sideways pressure into flex and skate; keep the cover square to the wall and let the pile deliver the paint rather than pushing. De-lint first: even a lint-free woven cover carries loose manufacturing fiber — tape-peel or wash-and-spin it before the first load, because you can't groom the film behind a radiator. Accept the finish standard of the location: hidden walls are coverage, not show — don't chase a lap-mark-free finish where no light will ever rake. Clean and keep: woven covers wash and reuse — scrape, rinse to clear water, spin, stand on end to dry.
Asked at the counter
BUYER QUESTIONS ANSWERED BEFORE THE CART, NOT AFTER THE RETURN
What's the 16-inch frame for?
Reaching walls you can see but can't get a hand to — behind radiators, toilet tanks, appliances, and into the backs of built-ins (§2a, §2b).
Is the cover any different from a normal mini?
No — it's a standard 4-inch, 15/32″ lint-free woven mini. The frame is what makes this SKU (§1, §5).
Can I finish a door or wall with it too?
Yes, competently — the long frame is just more handle than those need. It's a bonus, not the reason to buy it (§2c).
Why lint-free back there?
Because a shed fiber in a spot you can't reach to fix is a permanent defect — woven's interlocked yarn prevents it (§1).
How much paint should I load for hidden work?
Less than you think — you can't blot a drip you can't reach, and 15/32″ carries enough to run (§3).
Radiator too tall for 16 inches?
Step up to the 94003's 24-inch frame for deeper reach (§5).