Fluid flow, hydraulics, air brake fittings – the area is referred to by many names and can at times seem confusing, but it doesn’t have to be!
The hoses and fittings are integral in so many parts of life people take for granted. Like driving – or stopping – their car. And when these items fail, you need to get them fixed in a hurry.
Kimball Midwest is offering this small crash course in how to measure fittings so you can make sure you have the right ones when you need to replace them.
There are a few things you’ll need first, because it’s not as simple as taking out a ruler.
You must have the right gauges and a Kimball Midwest catalog or other reliable reference source. You may already have these, so feel free to look around your shop.
The first thing you must do is identify what the fitting is. Is it brass, steel, polymer, composite or something else?
The next thing you must identify is the style. Is it a pipe fitting coupler? A push connect elbow? A DOT male connector? Admittedly, this isn’t easy if you haven’t been trained. This is where the catalog comes in handy. Start in the fluid flow section and search to find something that looks like what is in your hand.
Now, you must identify the tube size and port size. To do this, you need to measure the fitting based on the way the part number is listed in the catalog, generally tube end first, port end last.
If it’s a male pipe thread (the threads are sticking out), drop it on a tube gauge dot. (A tube gauge has a dot representing a specific size of male pipe thread.) To determine the male pipe thread size, simply cover the corresponding dot that represents the outside diameter of the pipe thread.
Many tube gauges also have a series of half-circles across the edge that are used to measure several components.
If it is a female pipe thread (the thread indentations are cut into the part), using the half-circles, measure the opening that most closely corresponds and subtract 1/4".
Why do you subtract a quarter?
When the original standard was written by Joseph Whitworth in 1841, they were trying to determine what this size is. When they made tube fittings back then, they took 1/8” thick steel and rolled it to make the component. They didn’t want to use the material as part of the sizing, so they subtracted 1/8” from each side, giving you a total of 1/4” to reduce.
If it is a straight thread, measure the thread and go to a chart. The chart will likely be on the back of your tube gauge.
When measuring fittings, we need to determine tube size and port size. A simple method of finding the tube size for straight thread fittings is to measure the thread, like measuring a cap screw, then go to a chart.
Let’s say, for example, you have determined you are measuring a male 37 JIC fitting. Measure the outside diameter and go to the chart to find the corresponding Style (JIC), then go across the chart to find the measurement. Across the very top will be the tube sizing. So go across the fitting style row to find the measured size, then go to the top where tube size is identified.
Getting creative also is acceptable here. If you know your male end is 1/2” and it inserts and threads into the female end, you have your answer on what that measurement is.
Also, remember British Standard Pipe and National Pipe Thread will not engage with each other because of the flank angle and on certain sizes and having a different thread count. Always make sure you know what kind of pipe you are using, NPT or BSP. Also, BSP is available as BSPT (taper thread) and BSPP (parallel thread).
There is, however, a fitting that can be used for NPT, BSPP and BSPT known as the Uni-Max. This fitting will allow shops that have equipment from various countries to have one fitting for all pipe port applications.
Earlier this year, Kimball Midwest released two new fitting identification gauges to help with this process.
The BSPP and Metric Thread Gauge Kit and the JIC, NPT, ORB, ORFS Thread Gauge Kit both offer no-guesswork identification so you can quickly and accurately identify hydraulic fittings in the field or shop. These gauges allow you to identify internal and external threads, along with thread pitch, and both are conveniently packaged in a vinyl pouch for easy accessibility and storage.
These kits join the O-Ring Gauge in the Kimball Midwest line. This tool easily identifies O-ring sizes up to 13 inches inside diameter. It’s easy to store and made of a rugged composite material to ensure a long service life.
Even with the right tools, it’s still best to have an expert who can help make sure you have the equipment you need to make your hydraulic system safe and efficient. Just ask your Kimball Midwest sales representative for assistance, or, if you don’t have one, we can help you