Short definition
A tub spout delivers water to the bathtub. Two install styles cover almost all residential spouts: threaded (interior threads onto a 1/2-inch NPT brass nipple) and slip-on (chrome sleeve slips onto a copper stub-out, locked with an Allen-key set-screw). Verify which style your existing wall accepts before buying a replacement.
What it is
The two install styles:
- Threaded tub spout. Interior 1/2-inch NPT female threads match a brass nipple coming out of the wall. Spin onto the nipple by hand, then snug with a strap wrench. Common in older homes where the original install used iron piping.
- Slip-on tub spout. Interior chrome sleeve slips onto a copper stub-out projecting from the wall; a small Allen-key set-screw on the underside locks the spout in place against the copper. Common in modern installs where the rough-in is copper.
Both styles can be plain (no diverter) or include a diverter for the shower head — a lift-rod or push-button on the spout that closes the spout outlet and forces water up the riser to the shower head.
UPC 408.5 requires a 1-inch minimum air gap between the tub-spout outlet and the tub overflow rim — anti-backflow protection. Standard manufacturer recommendation is 4 to 6 inches above the tub rim, with 8 to 18 inches center-to-center between shower valve and tub spout for proper diverter back-pressure.
Cost:
- Slip-on tub spout: $15 to $30.
- Threaded tub spout: $20 to $60.
- Premium finish (matte black, brushed nickel): $40 to $120.
Why it matters to a homeowner
The single most common DIY tub-spout mistake: buying a threaded spout for a slip-on install (or vice versa). The two are not interchangeable.
Before buying, check what’s in the wall:
- Pull off the existing spout. Slip-on spouts have a small Allen-key set-screw on the underside; loosen it and slide off. Threaded spouts unscrew counterclockwise.
- Look at what’s behind it. A copper stub projecting straight from the wall = slip-on. A 1/2-inch brass nipple with visible threads = threaded.
- Buy the matching style. Universal “retrofit” tub spouts that fit either style exist — they cost a couple dollars more and are worth it if you’re not certain.
If you find a copper stub when you expected threaded (or vice versa), have a plumber convert with a brass nipple and elbow inside the wall — about $150 to $300 of plumbing work, less if a wall is already open during a remodel.
In WA hard-water areas, the spout outlet itself can scale up over years and restrict flow. A vinegar soak (unscrew the spout and submerge it for 30 minutes) often restores flow; replacement is the alternative.
Common failure modes
- Diverter failure (see diverter tub spout entry).
- Mineral scale at the spout outlet. Common in WA hard-water service.
- Loose set-screw on slip-on spout. Spout sags; tighten the set-screw.
- Cross-threaded threaded spout. Leak; replace the nipple or the spout.
Common variants
- Slip-on (set-screw, copper stub) vs. threaded (NPT nipple). The defining install distinction.
- Plain spout vs. diverter spout. Feature axis.
- Wall-mount tub spout (this entry) vs. floor-mount tub filler (for freestanding tubs). Different mounting hardware entirely.