Hose Clamp Size Chart: How to Measure and Pick the Right Clamp

Short answer: Measure the outside diameter of the hose where the clamp will sit, with the hose fully installed on its fitting. Choose a compatible clamp whose stated clamping range includes that measurement. The hose’s inside diameter, the pipe size and an SAE size number alone are not enough to choose a clamp.

Sizing a clamp for an intercooler boot? Our T-bolt clamp sizing guide covers Mammoth’s nine spring-loaded T-bolt sizes.

How to measure for a hose clamp

1. Work with the engine off and cool. Do not loosen a hot or pressurized coolant connection. Follow the vehicle’s service instructions before removing a hose.
2. Install the hose fully on its fitting. Measuring a loose hose can give a different result because the fitting can expand it.
3. Measure the installed outside diameter. Use calipers at the clamp’s intended seating position without squeezing the hose. Follow the hose or fitting maker’s instructions for clamp placement; do not measure across a raised bead and mistake that for the seating diameter.
4. Write down the measurement and units. Compare it with the actual range of the clamp you plan to buy, then check the clamp’s suitability for that hose and application.

No calipers? Wrap a non-stretch tape or strip of paper around the hose at the same location. Measure that circumference and divide by 3.1416 to estimate the diameter. For example, 160 mm around is about 50.9 mm across. Keep the wrap level and avoid pulling it tight enough to compress the hose.

How to read a clamp range

A marking such as 40–63 mm describes a diameter range, not the hose’s inside size. An installed diameter of 51 mm falls within that range. It falls outside a 21–44 mm range, even if both clamps look similar.

Also check how the clamp must be installed. It may need to pass over a larger part of the connection before reaching its seat. Follow the clamp maker’s installation method. Do not automatically buy a larger clamp to clear a bead: the chosen clamp still needs the correct working range and application approval at its final position.

If two ranges include your measurement, use the manufacturer’s selection guidance. There is no universal midpoint rule that replaces those instructions.

SAE hose clamp size chart: a named-series example

Numbered sizes such as #12 and #32 appear on many worm-drive clamps. Use the number to look up the exact product, not as a direct measurement of hose diameter. Different series can have different working ranges.

This reference shows selected sizes from Ideal Tridon’s Hy-Gear 67-6 series. It is not a Mammoth sizing chart and does not cover miniature, spring-band or T-bolt clamps.

Inch limits are the manufacturer’s published values. Millimeter figures here are calculated from those inch limits using 25.4 mm per inch, rounded to one decimal; they are not the manufacturer’s separately rounded metric specifications. For a purchase, use the exact product’s current specifications and installation instructions.

Mammoth hose clamp sizes

Our stainless steel hose clamps are listed by millimeter range. Use those listed ranges rather than assigning them an assumed SAE equivalent.

The inch values are rounded conversions. Check the product page for current availability in your size.

Our spring-loaded T-bolt clamps come in nine listed ranges, from 63–70 mm through 104–112 mm. See the full T-bolt size table rather than choosing by a rounded inch label. Both products are in our hose clamp collection.

Worm-gear or T-bolt?

A worm-gear clamp uses a screw to tighten its band. A T-bolt clamp uses a bolt and nut; a spring-loaded version includes a spring. Size is only one part of choosing between them.

Use the clamp construction specified for your hose and connection. In particular, do not assume every perforated worm-gear clamp is suitable for every silicone hose. Band design, hose material and installation requirements matter. Ideal Tridon, for example, offers lined clamps for silicone and other soft hoses. If a Mammoth kit includes clamps, use its supplied clamps and fitment instructions rather than substituting from a general chart.

Frequently asked questions

What size clamp does a radiator hose need?

Measure that hose’s installed outside diameter at the clamp seat, then check the vehicle or hose maker’s required clamp type. There is no single radiator-hose clamp size that fits every truck.

Does a 3/8-inch hose take a 3/8-inch clamp?

No. Hose sizes usually refer to the inside diameter, while the clamp goes around the outside. Wall thickness and the installed fitting affect that measurement. Do not assume Mammoth’s smallest 18–32 mm clamp fits a particular 3/8-inch hose without measuring. Our heater hose size guide explains inside-diameter sizing.

How tight should a hose clamp be?

Use the tightening instructions for the exact clamp and application. Do not borrow a torque value from another brand or clamp series. If that information is missing, ask before installation rather than tightening by guesswork.

Can I use the number on my old clamp?

It is a useful starting point if you can identify the manufacturer and series. Still check the replacement’s stated range and suitability, especially if the hose or fitting has changed.

Measure first, then choose your clamp

Have your installed outside diameter, hose material and application ready before ordering. Pick the appropriate range on the hose clamp or T-bolt clamp page. If you are unsure, contact Mammoth with those details so we can help narrow down the options.