Cushion Loop Clamps for Wire Bundles and Tubing
A cushioned loop clamp holds a wire bundle or tube to structure through a metal band lined with an elastomer cushion. General purpose clamps are bought to SAE AS21919, the successor numbering to MS21919, where letters code the band and cushion, W means wedge, and the size is the tube diameter in sixteenths of an inch.
Updated
Clamp types and where they are used
The clamp choice comes down to what is held, what fluid the cushion will see and how hot the zone gets. Most airframe and launch vehicle harness and line routing uses one of the families below.
| Type | Typical use | Usually bought to |
|---|---|---|
| Cushioned loop clamp, general purpose | Wire bundles and tube runs fastened to brackets and structure | SAE AS21919 (MS21919 part numbers on legacy drawings) |
| High performance cushioned loop clamp | Hydraulic lines, where the general purpose clamp is not intended | SAE AS85052 general specification |
| PTFE cushioned loop clamp | Positions where the drawing calls for a stainless band with a PTFE cushion | NAS1715 (stainless band with PTFE options) |
| Block or multi line clamp | Several parallel tubes held at a fixed spacing | OEM drawing or manufacturer part number |
AS21919 itself says the general purpose clamp is intended for general clamping, including electrical wire bundles, and points users to the MIL-C-85052 family for high performance clamps in MIL-H-5540 hydraulic systems. SAE now publishes that general specification as AS85052.
The specifications that govern loop clamps
| Document | What it covers | Status as verified |
|---|---|---|
| SAE AS21919 | Clamp, loop type, cushioned support: dimensions, band and cushion materials, marking, closure test | Active; a standards reseller shows the 2015 edition superseded by AS21919A in March 2017 |
| MS21919 | The original military standard for the same clamp; part numbers are still sold side by side with AS21919 numbers | Legacy designation; MS21104 and MS21105 were superseded by MS21919 |
| SAE AS85052 | Clamp assembly, loop type, cushioned, general specification | AS85052C revised July 2025 |
| MIL-C-85052A | Former military general specification for the same clamps | Superseded by MIL-DTL-85052B |
| NAS1715 | National Aerospace Standard loop clamp with stainless band and PTFE cushion options | Design holder National Aerospace Standards (CAGE 80205) |
| SAE AS478 | Marking method codes; AS21919 marks part number and manufacturer per AS478 method 2A1 | Referenced by AS21919 |
Material documents behind AS21919 include AMS 5510 for the Type 321 stainless band, AMS-QQ-A-250/5 for the 2024 aluminum band, AMS 3209 for chloroprene, AMS 3310 for silicone and MIL-R-25988 Type II for fluorosilicone. Order by the clamp part number, not by these material specs, but expect the manufacturer certificate to trace to them.
Have a part like this?Send it in under a minute. A person replies within 1 business day.How the AS21919 part number is built
AS21919 gives its own example, AS21919WDG08. Read it left to right:
| Field | Value | Meaning per AS21919 |
|---|---|---|
| Basic number | AS21919 | Clamp, loop, cushioned |
| Wedge | W | Wedge type cushion; omit the W for a non wedge clamp |
| Band | D | 2024-O aluminum, heat treated to T42, chemical conversion coated per MIL-C-5541 Class 1A |
| Cushion | G | Chloroprene per AMS 3209, black with a blue identifier |
| Size | 08 | Tube OD 0.500 in, which is 8 sixteenths |
The wedge is not optional. AS21919 makes it mandatory on sizes -02 through -48 and prohibits it on -01 and -50 through -66. A stiffening bead is required on sizes -06 through -24. Band thickness changes with size and material, from 0.020 in on the smallest clamp up to 0.062 in on larger aluminum clamps and 0.040 in on larger stainless ones, so a substitute clamp from another standard may not fit the same fastener stack.
Band and cushion codes, fluid limits and temperature
AS21919 allows only listed band and cushion combinations and gives a maximum recommended temperature for each. Do not specify a combination that is not on the list.
| Code | Band and cushion | Max recommended | Fluid notes from the standard |
|---|---|---|---|
| DE | Aluminum, ethylene propylene | 212 °F | For phosphate ester hydraulic fluid; not resistant to petroleum fluids; purple |
| DF | Aluminum, nitrile | 275 °F | Fuel immersion and fuel vapor; not for phosphate ester; not on titanium tubing; yellow |
| DG | Aluminum, chloroprene | 212 °F | General purpose, petroleum hydraulic fluid and occasional fuel splash; not for phosphate ester; not on titanium tubing |
| CE | Stainless, ethylene propylene | 275 °F | As DE |
| CF | Stainless, nitrile | 275 °F | As DF |
| CG | Stainless, chloroprene | 212 °F | As DG |
| CH | Stainless, silicone | 400 °F | Elevated temperature with phosphate ester and other synthetic fluids; not petroleum fluids; white |
| CJ | Stainless, fluorosilicone | 392 °F | Elevated temperature with petroleum fluids; not phosphate ester; blue |
The fluid columns matter more than the temperature column. A chloroprene cushion in a zone that sees phosphate ester hydraulic fluid will degrade, and an ethylene propylene cushion near fuel will too. Cushion color lets an inspector check the code on the aircraft without reading the band marking.
Band material is the second choice. Aluminum bands are light and suit most bundle clamping. Stainless bands are the only option for silicone and fluorosilicone cushions and are the usual choice near heat. The standard calls for the aluminum band to be chemical conversion coated and the stainless band to be passivated; contact between an aluminum band and stainless or titanium hardware is a dissimilar metal joint, so follow your program's rules for it. See the stainless and specialty steels and aluminum alloys pages for the base materials.
Spacing and installation for wire and tube routing
Clamp spacing and orientation come from the installation drawing, the airframe or vehicle standard practices and the harness or tubing specification. Do not let a supplier choose them. What the buyer controls is that the right clamp arrives for each position.
- Size to the bundle or tube, not to what is on the shelf. The D dimension in AS21919 equals the nominal tube OD. An oversized clamp lets the bundle chafe; an undersized clamp crushes the cushion and the outer wires.
- Respect the closure. AS21919 includes a closure test with the clamp on a bar of the nominal diameter, gap held within tolerance and mounting holes aligned within 0.010 in. If the holes will not align without force on the installed bundle, the clamp size or bundle diameter is wrong.
- Do not mark or rework the radius. The standard prohibits marking in the radius, and bending a band to make it fit voids the part.
- Check titanium lines. Nitrile and chloroprene cushions are not for use on titanium tubing under AS21919. Fluid lines in titanium need a different cushion code.
- Wire bundles near fluid lines. Routing separation rules belong to the installation drawing; the clamp only holds the bundle where the drawing puts it.
Block clamps for parallel tube runs come in several designs and are bought to the OEM drawing or the manufacturer's part number, and the PO should name the block material, bolt and nut part numbers and tube sizes per position.
What to put on the purchase order
- Full part number with W, band code, cushion code and size, for example AS21919WCJ12, and the standard revision your drawing accepts, AS21919 or AS21919A.
- Whether MS21919 numbered product is acceptable against an AS21919 callout, or the reverse. Get that in writing from engineering once and reuse it.
- Manufacturer name or CAGE code, and lot traceability on the certificate of conformance.
- Material certifications for the band and cushion when your quality clauses require them, traced to the material specs AS21919 names.
- Cushion cure or manufacture date where your program applies shelf life to elastomer products.
- DFARS specialty metals compliance for the stainless band on defense contracts; see DFARS specialty metals.
- Packaging: bagged and labeled by part number, quantity and lot, so mixed sizes cannot get combined.
Counterfeit and quality risks, and how to receive clamps
Loop clamps are cheap, which is why the risk is substitution rather than elaborate counterfeiting: a commercial clamp with a similar look, the wrong cushion compound, an aluminum band where stainless was ordered, or a missing wedge. At receiving:
- Check the band marking for part number and manufacturer or CAGE code, as AS21919 requires.
- Check the cushion color against the code: purple E, yellow F, black with blue identifier G, white H, blue J.
- Confirm the wedge is present on sizes -02 to -48 and bonded, not loose.
- Confirm the band material matches the code letter, aluminum for D and stainless for C, and that the certificate traces to the material specs AS21919 names.
- Measure D and band thickness on a sample against the standard's size table.
More on sampling is on the receiving inspection page, and on traceable sources on counterfeit parts avoidance.
How we source cushion clamps
We do not keep stock, publish prices or represent any clamp maker. We buy AS21919, MS21919, AS85052 and NAS1715 clamps through the manufacturer or its authorized and franchised distribution with lot traceability, flow your codes and paperwork requirements down, and deliver with a certificate package. Clamps can ride on the same PO as the brackets, tube assemblies or harnesses they hold, and we can kit them by installation position. For superseded or hard to find codes we run the search under our obsolete parts controls. Related: heat shrink and sleeving, caps and plugs, and the protection parts list.
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Questions
What does AS21919WDG08 mean?
Per AS21919, W is a wedge type cushion, D is a 2024 aluminum band heat treated to T42 and chemical conversion coated, G is a chloroprene cushion per AMS 3209, and 08 is the size code for a 0.500 in tube or bundle diameter, eight sixteenths of an inch. The standard recommends a maximum of 212 °F for the DG combination.
Is MS21919 the same clamp as AS21919?
AS21919 is the SAE standard that carries the MS21919 clamp forward, and distributors sell both part numbers for the same configurations. Whether you can accept one against a callout for the other is an engineering decision for your program, so get it approved once in writing and put it on the purchase order. Check which AS21919 revision your drawing accepts.
Which cushion should I use near Skydrol or other phosphate ester fluid?
AS21919 lists ethylene propylene (code E) for areas exposed to phosphate ester hydraulic fluid and silicone (code H, stainless band only) for elevated temperature with phosphate ester and other synthetic fluids. Nitrile, chloroprene and fluorosilicone cushions are listed as not resistant to phosphate ester fluids.
What is the hottest AS21919 clamp?
The CH combination, a stainless band with silicone cushion, carries the highest maximum recommended temperature in AS21919 at 400 °F. CJ, stainless with fluorosilicone, is listed at 392 °F and is the choice when the zone also sees petroleum based fluids. Where the drawing calls for a PTFE cushion instead, NAS1715 clamps are offered with a stainless band and PTFE cushion.
Can I use a cushion clamp on titanium tubing?
Not with every cushion. AS21919 states that nitrile (F) and chloroprene (G) cushions are not for use on titanium tubing. Pick a cushion code the standard allows for the tube material and fluid, or follow the clamp callout on the installation drawing, which should already reflect this.
Why does the wedge matter?
The wedge closes the gap at the clamp opening so the cushion fully surrounds the bundle or tube when the clamp is closed. AS21919 makes the wedge mandatory on sizes -02 through -48 and requires it to be molded or vulcanized to the cushion. A clamp without the wedge in that size range does not meet the standard.
Related
Sources
- UMPCO: AS21919 clamp, loop cushioned, catalog drawing with SAE notes (PDF)
- ANSI webstore: SAE AS21919 Clamp, Loop Type, Cushioned Support
- Standards.ie: SAE AS21919 edition status
- EverySpec: MS21104D superseded by MS21919
- SAE AS85052C Clamp Assembly, Loop Type, Cushioned, General Specification
- EverySpec: MIL-C-85052A status
- Boeing Distribution: NAS1715C8S stainless and PTFE loop clamp
- Military Fasteners: NAS1715C clamps
- Boeing Distribution: AS21919WDG07 chloroprene loop clamp
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