Compression Tube Fitting Reference Chart
Nut hex, makeup turns, and tube wall requirements for double-ferrule compression fittings from 1/8" through 1" OD. Compatible with Swagelok, Parker CPI/A-Lok, Ham-Let, and Hoke-style fittings.
Imperial Tube OD — Fitting Dimensions
| Tube OD | Nut hex (in) | Initial makeup (turns from finger-tight) | Min tube OD wall | Max tube OD wall |
|---|---|---|---|---|
| 1/8" | 5/16" | 3/4 | 0.020" | 0.035" |
| 1/4" | 9/16" | 1-1/4 | 0.020" | 0.065" |
| 3/8" | 11/16" | 1-1/4 | 0.028" | 0.083" |
| 1/2" | 7/8" | 1-1/4 | 0.028" | 0.083" |
| 5/8" | 1-1/16" | 1-1/4 | 0.035" | 0.095" |
| 3/4" | 1-1/4" | 1-1/4 | 0.035" | 0.109" |
| 1" | 1-5/8" | 1-1/4 | 0.049" | 0.120" |
Initial makeup: 1/8" tube — 3/4 turn from finger-tight. 1/4" OD and larger — 1-1/4 turns from finger-tight.
Re-tighten if leaking (fitting never disassembled): 1/6 turn (60°) additional. Do not exceed 1/6 turn without disassembling and inspecting the ferrules — ferrule deformation is irreversible.
Data represents Swagelok-style double-ferrule fittings (316 SS). Verify against specific manufacturer specs for safety-critical service.
Pressure ratings — 316 SS fittings with 316 SS tubing (room temp, psi)
| Tube OD | 0.028" | 0.035" | 0.049" | 0.065" | 0.083" | 0.095" | 0.109" | 0.120" | 0.134" | 0.156" | 0.188" |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/8" | 8,500 | 10,900 | — | — | — | — | — | — | — | — | — |
| 1/4" | — | 4,000 | 5,100 | 7,500 | 10,200 | — | — | — | — | — | — |
| 5/16" | — | — | 4,000 | 5,800 | 8,000 | — | — | — | — | — | — |
| 3/8" | — | — | 3,300 | 4,800 | 6,500 | 7,500 | — | — | — | — | — |
| 1/2" | — | — | 2,600 | 3,700 | 5,100 | 6,700 | — | — | — | — | — |
| 5/8" | — | — | — | 2,900 | 4,000 | 5,200 | 6,000 | — | — | — | — |
| 3/4" | — | — | — | 2,400 | 3,300 | 4,200 | 4,900 | 5,800 | — | — | — |
| 7/8" | — | — | — | — | 2,000 | — | 3,600 | 4,200 | 4,700 | — | — |
| 1" | — | — | — | — | 2,400 | 3,100 | — | 3,300 | 3,600 | 4,100 | 4,900 |
| 1-1/4" | — | — | — | — | 2,300 | 2,700 | 3,000 | 3,400 | 4,000 | 4,900 | — |
| 1-1/2" | — | — | — | — | — | 2,000 | 2,200 | 2,500 | 2,900 | 3,600 | — |
Column headers are wall thickness. Values are working pressure (psig) at room temperature for 316 SS fittings with annealed 316 SS seamless tubing (Rb ≤ 80). Ratings derate with temperature. Carbon steel and brass fittings have different ratings. Source: Swagelok tube fitting catalog. Verify with manufacturer for ASME/PED compliance and sour service.
Making up a compression fitting — field procedure
Initial Installation
- Cut and prep the tube. Cut square — no burrs, no angle. Tubing cutter for most industrial work; bandsaw and tube facer for aerospace and high-purity applications. Deburr ID and OD thoroughly.
- Assemble onto the tube. Slide nut onto tube with the threaded end facing the tube end. Slide on the back ferrule with the small, pointed end toward the body. Slide on the front ferrule with the larger, flat face toward the body.
- Insert and seat the tube. Push tube fully into the fitting body until it bottoms against the internal shoulder. Pull back slightly and push in again to confirm it is fully seated — it must stay bottomed throughout makeup.
- Finger-tighten and mark. Thread the nut onto the body finger-tight. High-pressure / safety-factor systems: further tighten until the tube will not turn by hand or move axially in the fitting. Before wrenching, make your reference marks: mark the nut at the 6 o'clock position to track rotation, and mark the tube at a distance from the tube end equal to the nut hex size (e.g., 1/2" OD tube → nut is 7/8" → mark 7/8" from end). If that insertion mark disappears into the fitting before you start wrenching, the tube has backed off the shoulder — reseat it.
- Tighten to position. Hold the body steady with a backup wrench — do not let it rotate. Tighten the nut: 1-1/4 turns to the 9 o'clock position for 1/4" OD and larger; 3/4 turn to the 3 o'clock position for 1/8" tube. Your 6 o'clock mark confirms the full turn count.
- Gauge check (if available). Position a Swagelok gap inspection gauge in the gap between nut and body. If the gauge does not enter the gap, the fitting is sufficiently tightened. If it enters, additional tightening is required.
Reassembly (Previously Swaged Ferrules)
- Mark before disassembly. Prior to taking the fitting apart, mark the tube at the back of the nut, and draw a line across both the nut and the fitting body flats. These marks are your reference for reassembly.
- Reinsert the tube. Insert the tube with the preswaged ferrules into the fitting body until the front ferrule seats against the body.
- Return to pulled-up position. While holding the body steady, rotate the nut with a wrench back to the previously pulled-up position — aligned with your marks. You will feel a significant increase in resistance at that point. Tighten slightly beyond that point only.