How it connects
A straight (parallel) thread, so the threads do not seal. The supply line's female coupling nut is turned on by hand, and a cone washer or flat gasket in the nut seals against the end of the shank.
Male and female halves
This is the male side: the fill valve shank sticking down through the tank's bottom hole. The female side is the supply connector's 7/8 in. ballcock coupling nut, often a plastic nut marked '7/8 BC'.
Usually connects to
- Matching nominal 7/8 in female ballcock supply-line nut, on braided/polymer line, with compatible cone washer
- Matching fill-valve shank locknut
- Matching swivel/PEX-to-ballcock adapter
Common sizes
- Common toilet shank: 7/8 in nominal, described as 15/16-14 UNS; other descriptions call it 7/8-14 or about 22.2 mm diameter.
- Some American Standard models use 3/4-16 UNF. Older/imported fixtures may use 1/2 in IPS shanks or 1/2 in nuts with adapters; these are different fits.
Where it is used
Residential/commercial gravity-flush toilet tanksFill valves and water-supply connectorsBidet T-adapters
Variations
- brass male adapters and flow restrictors
- American Standard 3/4-16 UNF alternative
- brass shank (e.g. Fluidmaster 400A)
- plastic shank (most modern fill valves)
- brass shank on older ballcocks
- supply line test plug with male ballcock thread
How to recognise it
A threaded shank about 24 mm across with fairly coarse threads (14 TPI), usually plastic, sticking out under the toilet tank. A large lock nut holds it to the tank, and the supply line's wing-shaped coupling nut screws onto it.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| 3/4 in. garden hose thread (GHT) | GHT is 1.0625-11.5, so it is coarser and larger; ballcock has 14 threads per inch. |
| NPT pipe thread | NPT is tapered and sealed on the threads. Ballcock thread is straight and sealed by a cone washer. 1/2 NPT is tapered, 14 TPI and about 0.84 in OD. The 7/8-14 ballcock thread is straight and about 0.875 in OD, and it seals with a washer, not on the threads. NPT is tapered with 14 TPI at ~0.84 in OD; the ballcock shank is straight and larger (~0.875 in), usually plastic. |
| 3/4-16 UNF American Standard toilet thread | Smaller (19 mm) and has 16 threads per inch. |
| 3/8 in compression | This is the other end of the toilet supply line, at the stop valve. It is much smaller and seals with a ferrule. |
Also called
7/8 in. ballcock thread; 7/8 in. ballcock shank15/16-14 UNStoilet fill valve shank thread; toilet fill valve inlet thread7/8 in toilet connection7/8-14 UNStoilet tank supply thread7/8" BC maletoilet tank inlet thread
Good to know
The 7/8-inch ballcock size is nominal; the actual thread is 15/16-14 UNS with a face gasket. Some American Standard models use 3/4-16 UNF instead.
Related connections
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