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

A worm-drive hose clamp gives you a variable-diameter, reusable, adjustable grip — but only if it is sized correctly to the hose it goes on. Too small and the band can't close; too large and you're relying on the very edge of the band's adjustment range, where the worm thread strips easily. The right clamp spans the actual hose OD with the band at roughly center adjustment, leaving room to re-torque if the hose compresses under load. This guide gives you the sizing chart and explains how clamp numbers translate to real diameter ranges.

Apex Flow Solutions stocks worm-drive clamps in 304 and 316 stainless and plated steel across the full size range from #4 through #64. The diameter ranges below are the SAE standard; confirm the range marked on the specific clamp before ordering.

In This Guide

• How Worm-Drive Clamps Are Numbered
• Worm Drive Clamp Sizing Chart
• How to Measure for the Right Size
• Clamp Position on the Barb
• Torque & Installation
• Material Selection
• Standards & References
• Frequently Asked Questions

How Worm-Drive Clamps Are Numbered

The SAE clamp number is based on the minimum diameter of the clamp's adjustment range in 1/16" increments. A #16 clamp has a minimum diameter of 16/16" = 1.000" and spans from 1" to 2" (the range is typically 1" wide for most SAE sizes). A #4 clamp spans from 4/16" = 0.250" to roughly 0.625". The number alone doesn't tell you the maximum — that depends on the band length and the manufacturer — so always read the marked range on the band. The chart below gives the standard SAE ranges for the most common sizes.

Worm Drive Clamp Sizing Chart

Match your hose OD (measured over the barb or fitting) to the clamp range. Select a clamp whose range brackets your hose OD near the center of its adjustment.

SAE clamp #	Min. diameter (in)	Max. diameter (in)	Min. diameter (mm)	Max. diameter (mm)	Common hose ID (std wall)
#4	0.25"	0.50"	6	13	1/8", 3/16"
#6	0.38"	0.63"	10	16	1/4"
#8	0.50"	0.75"	13	19	5/16", 3/8"
#10	0.56"	1.06"	14	27	3/8", 1/2"
#12	0.69"	1.25"	18	32	1/2", 5/8"
#16	1.00"	2.00"	25	51	3/4", 1"
#20	1.25"	2.25"	32	57	1", 1-1/4"
#24	1.50"	2.50"	38	64	1-1/4", 1-1/2"
#28	1.75"	2.75"	44	70	1-1/2", 2"
#32	2.00"	3.50"	51	89	2"
#40	2.50"	3.50"	64	89	2-1/2"
#48	3.00"	4.00"	76	102	3"
#56	3.50"	4.50"	89	114	3-1/2"
#64	4.00"	5.00"	102	127	4"

How to Measure for the Right Size

Do not use the hose ID or the barb nominal size to select a clamp. Use the actual outside diameter of the hose after it is pushed onto the barb or fitting. The hose stretches to fit over the barb ridges, increasing the OD compared to the bare hose. Measure with calipers or a pi tape at the point where the clamp will sit. Then select a clamp whose range brackets that OD near the center of adjustment — not at the tight or loose extreme.

Clamp Position on the Barb

Slide the clamp so the band sits over one of the barb's ridges — not in a valley between ridges and not past the last ridge onto bare fitting. Over a ridge, tightening the clamp drives the hose wall into the groove on both sides, creating two sealing lines and resisting axial pull-off. In a valley, the clamp merely squeezes the hose between ridges; over the end of the barb, there is nothing to resist pull-off. For most hose-barb joints, placing the clamp 1/4" to 1/2" from the end of the barb over the last ridge is correct.

Torque & Installation

Standard worm-drive clamps for soft hose (rubber, silicone) are typically tightened to 20–40 in·lb with a screwdriver or 5/16" hex driver. Smaller clamps (#4–8) are at the lower end; larger clamps (#16 and up) can take 40–60 in·lb. Check the manufacturer's recommendation. Over-tightening cuts the hose, especially soft silicone, and strips the worm screw or the screw housing on smaller clamps. Hand-tighten to resistance, then advance 1/4 to 1/2 turn past the point where the band stops slipping. On critical joints, check torque after the first pressure cycle — hose compression can relax and reduce clamp load.

Material Selection

Use 304 stainless for general outdoor and non-corrosive indoor service; 316 stainless for marine, coastal, chloride, or food/pharma service; zinc-plated steel only for dry indoor use. For the full decision guide on clamp materials, see our Hose Clamp Material Guide. Always verify the screw material on low-cost "stainless" clamps — many use a plated screw on a stainless band (the screw rusts first).

Standards & References

Worm-drive hose clamps follow SAE J1508, which defines clamp types (Type F = worm gear), size numbers, material classes, and test methods. The SAE size-numbering convention (number = min. diameter in 1/16" increments) is the U.S. standard and is used by virtually all domestic and imported clamps sold in the U.S. market. Stainless grades reference ASTM A240 for band material.

Frequently Asked Questions

What size hose clamp do I need for 3/4" hose?

Measure the hose OD over the barb — a 3/4" ID hose typically measures 1.00–1.10" OD over the fitting. A #16 clamp (range 1.00–2.00") is the usual starting point, with the band near the tight end of its range.

How do I know which clamp size to choose when there are two that fit my hose OD?

Choose the one that puts your hose OD closest to the center of the clamp's range. A clamp at its minimum adjustment can't be tightened further; at maximum, the screw housing is under stress.

Can I use a larger clamp and just tighten it all the way down?

No. A clamp wound to its maximum-closed position has the band at full overlap with the screw thread highly stressed. The worm screw can strip and the clamping force is inconsistent. Use the right size.

Does the clamp size number tell me the diameter?

Yes for the minimum: the number divided by 16 = minimum diameter in inches. A #10 clamp minimum is 10/16" = 0.625". For the maximum, read the range marked on the band or look it up in the SAE J1508 table.

Related Resources

• T-Bolt vs Worm Drive Clamps: When to Use Each — upgrade to T-bolt for high-pressure or silicone hose
• Hose Clamp Material Guide: 304 vs 316 vs Plated Steel — choose the right material for your environment
• Ear Clamp Installation, Tools & Sizing — for permanent, vibration-proof seals on small hose
• Technical Resource Center