Workshop / engineering

• Applying cutting oil or tapping fluid to drills, taps, dies, reamers and small milling cutters.
• Brushing coolant onto one-off manual machining jobs where flood coolant is not worth setting up.
• Applying layout fluid / marking blue.
• Applying light oil, way oil, slideway oil, spindle oil, anti-rust oil or WD-40 type products.
• Brushing swarf out of small pockets, threads, keyways, slots and drilled holes.
• Cleaning chips off vice jaws, parallels, collets and lathe toolposts.
• Applying anti-seize, copper grease or moly grease to bolts and threads.
• Applying thread-locker, retaining compound or gasket sealant where a cotton bud is too small.
• Cleaning around bearings, seals, circlip grooves and small housings with solvent/degreaser.
• Applying rust remover, phosphoric acid, blacking solution or other surface treatment chemicals.
• Brushing flux onto soldering, brazing or silver-soldering work.

Automotive / mechanical

• Applying brake cleaner/degreaser in awkward corners.
• Applying gasket cement, RTV, sealant or jointing compound.
• Applying grease to hinges, linkages, splines and small gears.
• Cleaning threads before assembly.
• Applying touch-up rust converter or cavity wax into small areas.
• Cleaning battery terminals or electrical connectors with contact cleaner.

Electrical / electronics

• Applying solder flux.
• Cleaning PCBs with IPA, especially for rougher work where a proper ESD brush is not needed.
• Applying conformal coating, potting compound or resin in small areas.
• Cleaning switchgear, relays, plugs and terminal blocks with solvent.
• Dusting out small enclosures, although bristle loss is a downside.

Adhesives / coatings

• Applying epoxy, contact adhesive, PVA, superglue accelerator, rubber solution or small amounts of resin.
• Spreading Loctite, bearing fit compound or sealant.
• Applying wood glue in joints, dowel holes and grooves.
• Applying stain, dye, wax, shellac or varnish where finish quality is not critical.
• Applying masking fluid or release agent.

Cleaning / detailing

• Cleaning threads, small holes, corners, mouldings and seams.
• Cleaning around machine nameplates, knobs, handles and castings.
• Cleaning jewellery, models, carburettors, airbrush parts or small mechanisms.
• Applying polish, metal cleaner or compound to small areas.
• Cleaning firearms would be a common US use, though I would avoid leaning on that in a UK listing.

Craft / hobby

• Model making: glue, resin, weathering washes, pigments, solvent cement cleanup.
• Leatherwork: dye, edge paint, contact adhesive.
• Ceramics: glaze touch-up or slip application.
• Candle/soap/resin work: release agent, colour, wax or resin application.
• General “use once and bin it” craft brush jobs.