Bending Basics, FAQs and Tutorials -

Choosing the Right Centerline Radius for Your Next Project

When it comes to selecting a centerline radius (CLR) for a die, there are two things to consider: minimum wall thickness specifications and design. Figuring out the minimum wall thickness specifications is the easy part. If you want to bend DOM mild steel or chromoly, those specs are listed in the die charts on our website. We break it down for each bender, each size material, and each centerline radius. If you want to bend ERW, we recommend going one gauge heavier on the wall thickness for quality bends. For other materials like aluminum or stainless, it’s a little more tricky, but we can help you out with that if you drop us a line. Sometimes, a single OD and wall thickness of your material, there’s only one centerline radius that can bend that material. Most times, you will have options. Then it’s time to consider design. We can help you figure out minimum wall thickness requirements, but figuring out your design is up to you.

One of the more frequent questions our technical sales team gets asked is, “What’s the most popular CLR in that OD?” For all of the common ODs, there usually is a popular CLR, but don’t let that influence your decision. Your project might be a little different than most guys, so it’s important to evaluate which CLR is best for your design, not the other guys’. Still, others might ask, “What’s the smallest CLR in that OD?” That might be important for some projects, but it’s important not to rush into getting the smallest CLR just because someone told you that’s what you need.

So how do you figure out which CLR is best for you? We’re going to show you! Whether you’re building a roll cage, a bumper, fenders, handrails, tuna towers, or anything for that matter, you want your bends to conform to the contour of where that tubing is going. For this example, we’re going to be choosing a CLR to build tube fenders for a Jeep Wrangler JK.

Tools Used:



-Compass with Pencil


So for about $10, you can figure out which centerline radius is best for you before you spend a couple hundred dollars on a die.


Here’s where the fender is going to go. We want the outside of the tubing to line up with the top corners of where the fender cutout is.


We’re going to use 1-1/4” OD, 0.095” Wall, ERW Round Tube. Here are the selection and specs for 1-1/4” OD Round Tube Dies. To figure out the inside radius and outside radius, subtract and add half the outside diameter to the centerline radius. Note: These values will change slightly when you take the tubing out of the die and it springs back, but these values are close enough for selecting your die. 


Centerline Radius (CLR)

Minimum Wall Thickness

Inside Radius

Outside Radius






















As you can see, the project isn’t bound by any wall thickness requirements. If we were bending 0.058” wall tubing, we couldn’t use a 4” centerline radius. But choosing this CLR is mainly about design now. So where do we start?


Step 1: Make templates for what a 90-degree bend would look like if you bent a piece of tubing in each of these dies using some paper. You can really use any material you like. We used poster board.


Step 1(a): Draw two perpendicular lines. Measure and mark your inside radius, centerline radius, and outside radius.


Step 1(b): Draw the inside radius with a compass.


Step 1(c): Draw the centerline radius with a compass. This step isn’t really necessary, but I like to see the centerline of the tubing. I draw it as a dashed line.



Step 1(d): Draw the outside radius with a compass.



This is what it should look like:


Step 1(e): Cut out your template. Make sure you label it. You’re going to have a handful of templates when this is done.



Step 2: Repeat steps 1(a)-1(e) for each size centerline radius.



Step 3: Line up all the templates where you want your bends to fit and choose the fit you want.


In this case, the 6” CLR is the best fit.


Step 4: Order your die! If you have any more questions about picking the right centerline radius for your next die, talk with one our expert technical salesmen who can point you in the right direction.


  • Brian

    .500" O.D x .065"WT, 304 Stainless Steel Tubing, I need to bend a perfect 3.250" Radius at 90 degrees, can you help me with info on the best type of bending machine I would need to eliminate twisting and marking of the material, I only would need to produce 10 of these per week.

  • Steve D

    I am a novice hobby fabricator totally flummoxed by bending math. These tutorials are clearing up the fog for me!
    Thank you!
    Steve D in DC

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