Most tube fittings go together the normal way: tube into the fitting body, nut finger-tight, then the manufacturer's specified turns. But there are jobs where setting the ferrules right there in the fitting body is the hard way to do it. That's where a pre-swaging tool earns its spot in your bag.
What Pre-Swaging Actually Does
Pre-swaging means making up the nut and ferrules onto the tube in a hardened tool body instead of in the fitting itself. The tool acts like a stand-in fitting body. You tighten, back off, and pull the tube out with the ferrules already set. Then you install that tube into the real fitting with much less effort.
The ferrules are swaged once, in a controlled spot, at the bench or on the floor where you can see what you're doing.
When It's Worth Reaching For
In my experience, these are the times pre-swaging pays off:
- Tight or awkward spots. Overhead runs, crowded instrument racks, or a fitting tucked behind a transmitter where you can't get a full swing on a wrench.
- Larger tube sizes. On 1/2" and up, initial make-up takes real torque. Doing it in a vise-held tool is safer for your knuckles and the system.
- Expensive components. Valves, manifolds and analyzer ports aren't something you want to strain on the first make-up. Pre-swaging keeps that work off the component.
- Shop prefab. If you're building tube runs at the bench to install later, pre-swaging lets you set ferrules in a clean, consistent setting.
Prep the Tube First
A pre-swaging tool won't fix a bad tube end. Cut it square with a cutter made for stainless, and hold the tube steady with the GRIP-IT TOOL so it doesn't spin in your hand. Then clean up the inside and outside edges with a deburring tool. Burrs and a crooked cut are behind a lot of the leaks I've chased over the years.
How to Pre-Swage the Right Way
- Bottom the tube fully in the tool. If the tube isn't seated, the ferrules set in the wrong spot and you'll fight that joint forever.
- Tighten to the turns the fitting manufacturer specifies for pre-swaging, then back the nut off and remove the tube. Most brands, like Dk-Lok, specify 1-1/4 turns from finger-tight.
- Look at the ferrules. They should be set evenly on the tube with no gouges or tilt.
- Install into the fitting body, snug it up, then add the manufacturer's specified turn for a pre-swaged connection.
When you're working on the fitting itself, the Fitting Tool holds stainless tube fittings from 1/16" to 1/2" steady so the body doesn't rotate while you tighten.
A Word on Gap Gauges
A gap inspection gauge is the quick way to confirm a first-time make-up got enough turns. Keep in mind many manufacturers say the gauge is meant for initial installations made in the fitting body, not pre-swaged or remade connections. Check your manufacturer's instructions so you're using the gauge where it applies.
Whether the connection was made up in the body or pre-swaged on the bench, a leak check works the same. Pressurize the line and put Gator Leak Detector on each fitting. Bubbles or a white foam show up in 5 to 30 seconds if there's a leak, and it dries clean without any residue. Depressurize before you make any correction.
Take Care of the Tool
Pre-swaging tools wear with use. Keep them clean, check them for damage, and replace them when they show wear. A worn tool sets ferrules poorly, and you won't know until something leaks.
You'll find pre-swaging tools, deburring tools, gap inspection gauges, the GRIP-IT TOOL and the Fitting Tool on our tools page. If you'd like hands-on help, our free Safety training course is open to new and existing customers.
Related reading: 5 Tube Fitting Installation Mistakes That Cause Leaks (and How to Avoid Them) and How to Safely Take Apart and Remake a Tube Fitting.
Need a Hand?
Not sure if pre-swaging is right for your job, or need the right tool for your fitting brand? Call A-Best Industrial Inc. Fittings, Valves, and Tubing at 310-833-3353 or email sales@abesttube.com. We're here Monday through Friday, 8:00 AM to 5:00 PM Pacific, with after-hours emergency service when you need it.