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Quick answer from a licensed plumber: Look under the spout at the wall end. A set screw in a small hole means a slip-on (slip-fit) spout that slides over a plain 1/2-inch copper tube and is held by that screw. No screw means a threaded (IPS) spout that screws onto a 1/2-inch threaded nipple. That is Moen’s test, and Delta labels its spouts the same way (“Slip onto 1/2″ C.W.T.” or “thread onto 1/2″ IPS”). Then match diverter or not, metal or plastic, and length.
Amazon-sold on September 24, 2026: Moen 3801 slip fit tub spout for a copper stub, or the Moen 3830 IPS tub spout / Delta RP17453 for a threaded nipple.
The 10-Second Test
Moen’s support article says it plainly: “There will be a small hole in the bottom of the tub spout, if you see a screw, you have a CC (Slip Fit) tub spout. If there is no screw, you have an IPS (threaded) tub spout.” The slip-fit screw takes a 5/32-inch hex wrench; the threaded spout has “No Hex screw.” Moen adds that “All Moen tub spouts attach to a 1/2″ diameter pipe,” and its Amazon listings say the same thing in more words: slip-fit spouts “can be identified by a set screw located on the underside of the spout near the wall,” while IPS spouts “typically do not have a set screw” there and “install onto a threaded pipe connection rather than a smooth copper pipe.”
| Slip-on (slip-fit, “CC”) | Threaded (“IPS”) | |
|---|---|---|
| What you see underneath | A small hole with a set screw | No screw |
| What it fits | Plain 1/2-inch copper tube sticking out of the wall (Delta: “Slip onto 1/2″ C.W.T.”) | A 1/2-inch threaded nipple (Delta: “thread onto 1/2″ IPS”) |
| How it comes off (Moen) | “Loosen the Hex screw until the tub spout slides off” | “Unthread the tub spout counter-clockwise to remove” |
| How it seals | An O-ring inside the spout on the copper | Pipe threads with tape or sealant |
Three More Things to Match (Moen’s List)
Moen’s “Types of Tub Spouts” article lists four things to know “before ordering or purchasing a replacement tub spout,” and the connection is only the last one:
- Diverter or non-diverter. “A diverter tub spout will have a lift rod that you pull up and push down on to divert the water between the showerhead and tub spout. A non-diverter tub spout will not have a lift rod (generally, used in a tub only or a three handle tub and shower configuration).”
- Metallic or non-metallic. Moen’s test: tap it with a metal spoon. Metal makes “a “clanking” noise”; a non-metallic spout makes “a “thud” sound.” Delta’s RP5834 is listed as “Plastic construction”; Moen’s 3800 is “Crafted from metal with a chrome-plated finish.”
- Length. “Moen manufactures tub spouts in different lengths to accommodate the reach needed for the tub.” Moen’s 3931, 3926 and 3801 are all listed at 5 1/2 inches; the 3830 is about 7 inches. Delta lists the RP17453 at 5 1/4 inches and the RP5834 and RP19820 at 5 1/2.
- Connection type. The screw test above.
Delta: Same Spout, Two Connections
Delta sells the same pull-up and pull-down diverter spouts in both styles, and the product page says which. The RP19820 pull-up diverter is a slip-on: “Slip onto 1/2″ C.W.T.” The RP17453 pull-down diverter is the other kind, and it accepts either a sweat or a threaded connection: “Sweat onto 1/2″ C.W.T. or thread onto 1/2″ IPS,” 5 1/4 inches long. The RP5834 pull-up diverter is a 5-1/2 inch plastic spout; Delta’s page does not print the connection, and its Amazon listing says “Sweat onto 1/2″ CWT or Threat onto 1/2″ IPS” [sic], so treat it as a threaded-or-sweat spout, not a slip-on.
Delta also sells adapters, which is how a slip-on Delta spout ends up on a threaded nipple or a short copper stub:
- RP12307 “Adapter w/ O-Ring – Tub Spout.” Delta’s staff answer on the part page gives the geometry: “The copper pipe should be a maximum of 3 1/2″ in length from the wall. The RP12307 Adapter Assembly should be installed 1/2″ to 1 1/4″ from wall.”
- RP33794 “Adapter – Tub Spout – Slip-On Diverter.” Delta’s listing: “Designed specifically for Delta tub spouts that use the RP33794 or RP12307” and “Not appropriate for all Delta tub spouts.” Delta staff on the page name the RP64721 as a compatible spout.
- RP100154 “Tub Spout Adapter – Tri Universal,” a brass adapter “Designed to adapt to threaded pipe on Delta slip-on diverter tub spouts” and “best suited for copper plumbing,” which Delta lists for the Woodhurst T14032, T14232 and T14432 trims.
I send an occasional note when a new guide goes up — repairs worth doing yourself, and the parts that actually last. No spam, no course funnel; written by a licensed Georgia plumber.
Moen: The Model Number Says Which
Moen sells its 5 1/2-inch diverter spout in both connections under different numbers: the 3931 is “Connection Type Slip Fit,” the 3926 is “Connection Type Ips,” both “Connection Size 1/2″” and “Tub Spout Type Diverter.” The 3808 is another slip-fit diverter spout. On Amazon, Moen’s own listings carry the identification in the bullets: the 3801 is “1/2-INCH CC SLIP FIT CONNECTION” on “compatible 1/2-inch copper pipe,” the 3800 listing tells you to “VERIFY IPS THREADED COMPATIBILITY,” and the 3830 is “1/2-INCH IPS THREADED CONNECTION” and about 7 inches long. Moen also sells the diverter’s wear part alone, the 101237 “Cup Seal & Diverter Gate” for the 3800 spout, if the spout is fine but the diverter no longer holds.
Which One to Buy When the Pipe Is Wrong
- Copper stub, want a slip-on: measure the stub. Delta’s adapter rule (copper no more than 3 1/2 inches from the wall) is the useful benchmark; a longer stub gets cut, a shorter one may need the adapter set closer to the wall.
- Threaded nipple, want a slip-on spout: Delta’s RP100154 adapts “threaded pipe on Delta slip-on diverter tub spouts”; otherwise buy the IPS version of the spout (Moen 3926 / 3830, Delta RP17453).
- Copper stub, want a threaded spout: Delta’s RP17453 can be sweated onto 1/2-inch copper (“Sweat onto 1/2″ C.W.T.”), which is a soldering job, or the stub can be fitted with a threaded adapter.
- Diverter leaks but the spout is fine: on a Moen 3800 the 101237 cup seal and gate is the part; on most other spouts the diverter is not sold as a separate part and the spout is replaced; check the maker’s parts page for your model. Our shower diverter repair guide covers the symptoms.
FAQ
How do I know if my tub spout is slip-on or threaded?
Look underneath at the wall end. Moen says a small hole with a set screw means a slip-fit (CC) spout; no screw means a threaded (IPS) spout. Slip-fit spouts slide onto a plain 1/2-inch copper tube; threaded spouts screw onto a 1/2-inch threaded nipple.
What size pipe does a tub spout fit?
Moen says all its tub spouts attach to a 1/2-inch diameter pipe. Delta lists its spouts as slip onto 1/2-inch copper (C.W.T.) or thread onto 1/2-inch IPS.
Can I put a slip-on tub spout on threaded pipe?
With an adapter or a different spout. Delta sells the RP100154 tri-universal adapter to adapt threaded pipe to its slip-on diverter spouts; otherwise buy the IPS version of the spout, such as the Moen 3926 or 3830 or the Delta RP17453.
How long should the copper stub be for a slip-on tub spout?
Delta’s guidance for its RP12307 adapter is a copper pipe no more than 3 1/2 inches from the wall, with the adapter installed 1/2 to 1 1/4 inches from the wall. Check the instruction sheet for the spout you buy.
Is the Moen 3931 slip fit or IPS?
Slip fit. Moen lists the 3931 with a 1/2-inch slip fit connection and the 3926 with a 1/2-inch IPS connection; both are 5 1/2-inch diverter spouts.
Why Trust Plumbing Picks
Plumbing Picks is written by a licensed Georgia journeyman plumber. Every part number, model list, size, setting and fit on this page comes from the manufacturer pages and documents listed below, which we opened and read; product details come from those makers and from the Amazon listings, not from hands-on testing. Each linked product was shipped or sold by Amazon, new and in stock, when we checked on September 24, 2026. Where a link goes to Amazon we may earn a commission at no extra cost to you. Nobody pays to be included here. More on who writes this and how we pick.
Sources
- Moen Solutions: Types of Tub Spouts
- Moen Solutions: Replacing a Tub Spout
- Moen: 3931 tub diverter spout, 1/2″ slip fit
- Moen: 3926 tub diverter spout, 1/2″ IPS
- Moen: 3808 slip fit diverter spout
- Delta: RP19820 Tub Spout, Pull-Up Diverter
- Delta: RP17453 Tub Spout, Pull-Down Diverter
- Delta: RP5834 Tub Spout, Pull-Up Diverter
- Delta: RP12307 Adapter with O-Ring, Tub Spout
- Delta: RP33794 Adapter, Tub Spout, Slip-On Diverter
- Delta: RP100154 Tub Spout Adapter, Tri Universal
Bottom Line
Screw underneath: slip-on, 1/2-inch copper. No screw: threaded, 1/2-inch IPS. Buy the same connection, the same diverter type and about the same length, and use Delta’s adapters only where the pipe and the spout you want do not match.