Worm Drive Clamp Sizing Chart: Hose ID to Clamp Range | Apex Flow

A worm drive clamp only seals reliably when its adjustment range brackets the actual clamping diameter — the hose wall plus the barb or fitting underneath it. Pick a clamp by SAE number off a guess and you end up either bottomed-out or barely engaged. This chart maps SAE clamp sizes to their real diameter ranges in inch and metric, and shows how to land your target diameter in the middle of the range where the clamp performs best.

Apex Flow Solutions stocks worm drive clamps in stainless and plated steel across the full SAE size range. Use the chart below to match clamp size to your assembly.

Clamping over a barb fitting?

Remember to size for the hose outside diameter once it is stretched over the barb, not the hose ID. Contact our team with your hose and barb sizes and we will confirm the clamp.

How Worm Drive Clamps Are Sized

Worm drive clamps (also called worm gear or hose clamps) are sized by an adjustment range, not a single diameter. The SAE numbering system assigns each clamp a size number — SAE 4, SAE 6, SAE 8, and so on — and each number corresponds to a minimum and maximum clamping diameter. The correct clamp is the one whose range places your target diameter near its center, leaving room to tighten without bottoming the band and without running out of thread.

The target diameter is the clamping diameter: the hose outside diameter after it has been pushed over the barb or fitting. It is not the hose inside diameter. A 1/2" ID hose with a 1/8" wall stretched over a barb can present a clamping OD well over 3/4", so always work from the assembled OD.

Worm drive hose clamp securing a rubber hose over a barbed fitting

The clamp must seal on the hose OD over the barb. Size so this assembled diameter sits in the middle of the clamp's adjustment range.

SAE Size to Clamp Range Chart

Common worm drive clamp SAE sizes and their nominal diameter ranges. Ranges vary slightly by manufacturer; verify against the product spec.

SAE Size	Min Diameter (in)	Max Diameter (in)	Range (mm)
SAE 4	7/32"	5/8"	6–16
SAE 6	5/16"	7/8"	8–22
SAE 8	7/16"	1"	11–25
SAE 10	9/16"	1-1/16"	14–27
SAE 12	11/16"	1-1/4"	17–32
SAE 16	13/16"	1-1/2"	21–38
SAE 20	13/16"	1-3/4"	21–44
SAE 24	1-1/16"	2"	27–51
SAE 28	1-5/16"	2-1/4"	33–57
SAE 32	1-9/16"	2-1/2"	40–64
SAE 40	2-1/16"	3"	52–76
SAE 48	2-9/16"	3-1/2"	65–89

Hose ID to Recommended Clamp Chart

A practical starting point for common rubber/PVC hose with a typical wall thickness, clamped over a matching barb. Confirm the assembled OD before final selection.

Hose ID	Approx. Assembled OD	Recommended SAE Size
1/4"	~1/2"	SAE 4
3/8"	~5/8"	SAE 6
1/2"	~3/4"	SAE 8
5/8"	~7/8"	SAE 10
3/4"	~1"	SAE 12
1"	~1-1/4"	SAE 16
1-1/4"	~1-1/2"	SAE 20
1-1/2"	~1-3/4"	SAE 24
2"	~2-1/4"	SAE 28

How to Size for Your Assembly

Follow these steps for a clamp that seals and stays sealed:

Measure the assembled OD: Push the hose fully onto the barb, then measure the outside diameter of the hose over the barb with a caliper or wrap a flexible tape around it and divide circumference by π.
Center the range: Choose the SAE size whose range puts your measured OD near the middle. Mid-range gives even band pressure and avoids both bottoming out and thread run-out.
Avoid the extremes: A clamp tightened near its minimum buckles the band; one near its maximum has too few threads engaged and can slip under vibration.
Match band width to hose: Use a wider band (1/2" or 9/16") on larger, higher-pressure hose and a narrow band (5/16") on small, soft tubing to avoid cutting in.

Chart illustration showing target diameter centered within a clamp adjustment range

Land your assembled diameter near the center of the clamp's range — not at the minimum or maximum — for even sealing pressure.

Band Width & Material Notes

Standard worm drive clamps use a 1/2" (12.7mm) band; micro/mini clamps use 5/16" (8mm) for small tubing. Material matters for both corrosion and strength: all-300-series stainless (band, housing, and screw all 304 or 316) resists corrosion best, while "partial stainless" clamps use a stainless band with a plated-steel screw that can rust in wet service. For marine and chemical exposure, specify all-316. The clamp material selection is covered in depth in the related material guide below.

Standards & References

Worm drive hose clamp dimensions and SAE size designations follow SAE J1508 (hose clamp specifications), which defines clamp types and the size-number ranges. Stainless band material grades reference ASTM A240 (304/316 sheet and strip). For potable or food contact applications, confirm the clamp meets the relevant FDA or NSF material requirements. Always torque the screw to the manufacturer's spec — over-torquing strips the worm gear or cuts the hose.

Frequently Asked Questions

What size hose clamp do I need for a 1/2 inch hose?

For 1/2" ID hose over a matching barb, the assembled OD is usually around 3/4", which falls in the middle of an SAE 8 clamp's range (7/16"–1"). Always confirm by measuring the assembled OD.

Do I size a hose clamp by the hose ID or OD?

By the assembled outside diameter — the hose OD once it is stretched over the barb or fitting. The clamp tightens on the outside, so the ID alone will undersize the clamp.

What does the SAE number on a hose clamp mean?

The SAE size number (e.g., SAE 8, SAE 16) designates a specific minimum-to-maximum clamping diameter range defined in SAE J1508. Higher numbers cover larger diameters.

Why does my hose clamp keep leaking or slipping?

Usually the clamp is at the extreme end of its range — bottomed out at minimum or barely engaged at maximum — or the band is too narrow for the hose. Re-size so the diameter sits mid-range and match band width to the hose.

Are worm drive clamps reusable?

Yes, within reason. As long as the band is not deformed and the worm gear threads are intact, a stainless worm drive clamp can be loosened and reused. Replace any clamp with a cut band or stripped screw.

Shop related products: Worm Drive Clamps | Hose Clamps