When a tech orders tubing, the outside diameter usually gets all the attention. That makes sense, because the OD has to match the fitting. But the wall thickness matters just as much. It decides how much pressure the line can hold, how well the ferrules grip, and how hard the tube is to cut and bend in the field.
Start With Your Working Pressure and Temperature
The pressure a tube can safely hold depends on its OD, wall thickness, material and temperature. A heavier wall holds more pressure at the same OD. Heat lowers the rating, so a line that is fine at room temperature may need a heavier wall on a hot process.
Don't guess. Use our fractional stainless tubing pressure chart, find your OD, and pick a wall that covers your maximum working pressure at your maximum temperature, with margin. For example, 1/2" seamless stainless is rated 2,400 psig at 0.035" wall and 6,200 psig at 0.083" wall. It also lists welded and high-temperature derating factors. A heavy-wall tube doesn't help if the valve or fitting downstream is rated lower.
Stay Inside the Fitting Maker's Wall Range
Compression fittings are designed for a range of wall thicknesses at each OD. Go too thin and the ferrule can push the tube inward instead of biting into it, and the connection may not hold under pressure or vibration. Go too thick and the fitting may not swage the tube properly. Check the minimum and maximum wall listed by the manufacturer before you order.
Hardness matters too. Instrument tubing should be fully annealed and within the hardness the fitting maker calls for. Hard tubing fights the ferrule and is a common cause of leaks that seem to come out of nowhere.
Wall range and hardness matter no matter whose fittings you use. If your plant already runs Swagelok and you're adding DK-Lok, DK-Lok had intermixed DK-Lok and Swagelok nuts, front ferrules, back ferrules and bodies tested to ASTM F1387 on 1/4" through 1" OD tubing, witnessed by TÜV Rheinland. The tests included pneumatic and hydrostatic proof, burst, vibration, rotary flex and repeated assembly, and no failures were observed. DK-Lok backs it with a written intermix guarantee for same-size, same-material Swagelok components that are properly assembled. You can read the full ASTM F1387 intermix test report here.
Thicker Wall Means More Care When You Cut
Heavy-wall stainless takes more turns to cut and leaves a bigger burr. Use a sharp wheel made for stainless, like our RIDGID tube cutters, and tighten a little at a time so you don't flatten or work-harden the end.
Stainless tube likes to spin in your hand while you cut. The GRIP-IT TOOL locks onto 1/8" through 1" OD tubing and holds it still, so you get a square cut without fighting the tube.
After the cut, clean up the inside and outside edges with a deburring tool. A heavier wall leaves more material to remove, and any burr left behind can keep the tube from seating on the fitting shoulder.
Thicker Wall Is Harder to Bend
A heavy wall resists bending more and can spring back further than you expect. Use a bender sized to your tube OD, pull with steady pressure, and check your angle before you move on. Our RIDGID tube benders come in 1/4", 3/8" and 1/2" sizes.
If the job has a lot of bends and the pressure doesn't call for heavy wall, a standard wall is often easier to install well. That is a good conversation to have before the order goes in, not after the tube is on the rack.
What to Put on the Order
To get the right tube the first time, list the OD, wall thickness, material grade, seamless or welded, and the length or coil you need. You can see what we stock, including 316/316L and 304/304L DFARS compliant stainless, on our tubing page, and find the cutters, benders and prep tools on our tools page.
We're Here to Help
Not sure which wall fits your pressure, temperature and fittings? Call A-Best Industrial Inc. Fittings, Valves, and Tubing at 310-833-3353 or email sales@abesttube.com. We'll help you match the tube to the job.