Short definition
A packing nut is the small nut, between the bonnet and the handle on a compression faucet, that compresses a packing washer (or graphite string) around the stem. Its job is to stop water from leaking up around the stem and out under the handle when the faucet is open.
What it is
In a compression faucet, the stem rises and falls inside the body each time the handle turns. Around the stem, where it exits the body, sits a packing washer or a wrap of graphite-impregnated string. The packing nut sits on top of that packing and screws down — compressing the packing radially against the stem, sealing the gap.
In British English, the same component is called a gland nut. Standard sizes on residential compression stems are smaller than the bonnet that surrounds them — typically 5/8 to 7/8 inch hex.
Why it matters to a homeowner
The classic compression-faucet symptom: water seeping up around the handle when the faucet is open. The first move is a quarter-turn tightening of the packing nut. That re-compresses the packing against the stem and often stops the leak without disassembly. If a quarter-turn doesn’t fix it (or the handle gets stiff before it stops leaking), the packing itself has flattened and needs replacing — a $0.50 packing washer or a few inches of graphite string.
Outdoor sillcocks use the same component and the same first-fix. If your hose bib drips at the handle when running, snug the packing nut.
When you over-tighten a packing nut, the stem binds and the handle gets hard to turn. Back it off slightly; if it still leaks, replace the packing instead of cranking harder.
Common variants
- Packing nut vs. bonnet nut. Bonnet retains the stem in the body. Packing nut sits inside (or just above) the bonnet and compresses packing around the stem.
- Packing nut vs. compression nut. Compression nut is on supply tubing — entirely different component despite the shared word.
- Packing washer vs. packing string. Modern faucets use a molded rubber or fiber washer; older two-handle bodies use graphite or hemp string wound around the stem.