Strut Pipe & Cushion Clamp Sizing Guide
Strut pipe clamps look simple, but picking the wrong type means a loose or crushed fit. The trick is matching the clamp to how your pipe is measured — conduit by trade size and type, tube by exact outside diameter. This guide shows how to choose, with OD reference tables for EMT, rigid, and copper.
Which Clamp Type?
| Clamp | Use For | Sized By |
|---|---|---|
| Universal | EMT or rigid (both) | Trade size; specify EMT or rigid for best fit |
| EMT | EMT thin-wall conduit | EMT trade size |
| Rigid | Rigid / IMC conduit, steel pipe | Rigid trade size |
| OD | Any pipe or tube | Measured outside diameter |
| Copper tube | Copper tube (copper-plated) | Copper tube size |
| Cushion | Vibration / dissimilar metals / movement | Pipe or OD, with plastic insert |
Rule of thumb: a universal clamp covers both EMT and rigid, but for the tightest hold order the clamp that matches your conduit type. When unsure, measure the actual outside diameter and use an OD clamp.
Conduit & Tube Outside Diameter Reference
EMT and rigid differ in OD at the same trade size, which is why the clamps differ:
| Trade Size | EMT OD | Rigid / Steel Pipe OD | Copper Tube OD |
|---|---|---|---|
| 1/2" | 0.706" | 0.840" | 0.625" |
| 3/4" | 0.922" | 1.050" | 0.875" |
| 1" | 1.163" | 1.315" | 1.125" |
| 1-1/4" | 1.510" | 1.660" | 1.375" |
| 1-1/2" | 1.740" | 1.900" | 1.625" |
| 2" | 2.197" | 2.375" | 2.125" |
Copper OD shown is nominal tube OD (size + 1/8"). For exact OD pipe and tube not listed here, order an OD clamp to the measured diameter.
Common Clamps
EMT: STR4311 (1/2"). Universal: STR4302 (3/4"), STR4305 (1-1/2"). Rigid: STR4322 (1/2"). OD: STR4341 (3/8" OD). Cushion: STR4413 (1/2" pipe), STR4434 (1/2" OD tube).
When to Use a Cushion Clamp
Choose a cushion clamp — with its plastic insert — when the line vibrates (pumps, compressors, hydraulics), when you are clamping dissimilar metals like copper on steel (the cushion prevents galvanic corrosion), or when the pipe needs to move quietly with thermal expansion. For static, same-metal runs a standard clamp is fine. See cushion clamps.
Brand Cross-Reference
| EFS SKU | Description | Unistrut | PowerStrut | B-Line |
|---|---|---|---|---|
| STR4322 | 1/2 rigid clamp | P1111 | PS 1100 1/2 | B2008 |
| STR4311 | 1/2 EMT clamp | P1426 | PS 1000 1/2 | B2001 |
| STR4341 | 3/8 OD clamp | P2025 | PS 1200 3/8 | B2024 |
Full chart: Strut Brand Cross-Reference.
Frequently Asked Questions
What is the difference between an EMT clamp and a rigid clamp?
EMT (thin-wall) and rigid (heavy-wall) conduit have different outside diameters at the same trade size, so the clamps are sized differently. A universal clamp fits both, but for the tightest hold use the clamp that matches your conduit type. The OD reference table above shows the difference.
Can a universal clamp be used for both EMT and rigid?
Yes. The universal clamp is designed to fit both EMT and rigid conduit at a trade size. It is the convenient single-SKU option; order a dedicated EMT or rigid clamp when you need the most precise fit.
How do I size a clamp for plain pipe or tube?
Measure the actual outside diameter and order an OD clamp to that diameter. OD clamps come in fine increments, so you can match almost any pipe or tube exactly.
When should I use a cushion clamp instead of a regular clamp?
Use a cushion clamp when the line vibrates, when clamping dissimilar metals such as copper on steel, or when the pipe must move quietly with thermal expansion. The plastic insert damps vibration and prevents galvanic corrosion. For static same-metal runs a regular clamp is fine.
Related Guides
- Strut Channel Accessories Guide
- Strut Brand Cross-Reference
- Shop Pipe & Conduit Clamps
- Shop Cushion Clamps