What Size Replacement Pump Fits My Bottle? 28/400 vs 33/400 vs 38/400

Short answer: the first number is the neck diameter in millimetres. The second number (almost always 400) is the thread style. A 33/400 pump fits a bottle with a 33 mm opening and 400-series threads. Measure straight across the outside of your bottle’s opening, rim to rim, and match the millimetres.

The quick match chart

Neck size	Measure across the rim	Typically fits
28/400	28 mm (about 1–1/8″)	Slimmer 32 oz amber bottles, most spray bottles
33/400	33 mm (about 1–5/16″)	32 oz Boston round bottles — the most common soap & shampoo bottle
38/400	38 mm (about 1–1/2″)	Gallon and half-gallon jugs, detergent bottles
48 mm	48 mm (about 1–7/8″)	Glass milk bottles — takes a pour spout, not a pump

What the two numbers actually mean

Closure sizes are written as two numbers separated by a slash, like 33/400.

• The first number is millimetres. It is the outside diameter of the bottle’s opening, measured across the threads. 33/400 means a 33 mm opening.
• The second number is the thread finish. 400 is a single-lead, shallow thread — the standard on almost all household bottles. You will occasionally see 410 or 415, which are taller threads that need more turns to close.

This is why a pump that looks identical to yours may still not fit. A 28/410 and a 28/400 are both 28 mm across, but the thread pitch differs and the pump will cross-thread or sit loose.

How to measure your bottle in ten seconds

1. Take the cap or old pump off.
2. Lay a ruler across the top of the opening, rim to rim — the outside edge of the threads, not the inner hole.
3. Read the millimetres. If you only have an imperial ruler: 1–1/8″ ≈ 28 mm, 1–5/16″ ≈ 33 mm, 1–1/2″ ≈ 38 mm, 1–7/8″ ≈ 48 mm.
4. Round to the nearest size in the chart above. Necks are manufactured to these standards, so you will land on one of them.

The most common mistake: measuring the inside of the opening instead of the outside. That will read 3–5 mm small and send you to the wrong pump.

Why the dip tube length matters too

A pump can thread on perfectly and still not work. The dip tube — the straw that runs to the bottom — has to reach the bottom of your bottle. A pump made for a short 8 oz bottle will thread onto a 32 oz bottle and draw nothing but air.

Most dip tubes can be trimmed shorter with scissors. None can be made longer. When in doubt, buy the pump sized for your bottle rather than trimming one down from a much taller bottle.

Milk bottles are different

Glass milk bottles use a wider 48 mm opening and generally do not take a pump at all — they take a pour spout or a lid. If that is what you are looking for, you want a 48 mm pour spout (from $11.99) or the silicone pour spout in six colours ($21.99 for a 6-pack).

Still not sure?

Send us a photo of your bottle opening with a ruler across it and we will tell you which pump you need. Email support@kitchentoolz.com — a real person answers, usually the same day.

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