How to measure hose crimp diameter

Crimp diameter is the outer diameter of the ferrule after crimping, measured with calipers. The target comes from the fitting maker’s table and changes with each hose, fitting and die pair. Put the calipers on the flat part of the ferrule, off the ridges, at two opposite points; a reading within tolerance means a good crimp.

What is crimp diameter and why measure it?

Crimp diameter is the outer diameter of the fitting after crimping. When it is right the fitting grips the hose and holds the pressure. If the diameter stays too large (under-crimp) the fitting can pull off the hose; if it closes too far (over-crimp) the braid and body of the hose are damaged. So measure the first parts on any new hose, fitting and die combination, then sample parts at regular intervals.

Where do I find the target crimp diameter?

The target is in the fitting maker’s crimp table. The table changes line by line with hose type, inner diameter, fitting code and die set; do not apply one maker’s table to another maker’s fitting. If you cannot get the table, send us the fitting code and the hose type and we will help you with the die choice.

How do I measure with calipers?

1. Close and zero the calipers; keep the jaws and the ferrule clean.

2. Find the flat zone in the middle of the ferrule; the jaws must not touch the ridges.

3. Read at two opposite points. If your maker asks for it, turn the ferrule 45 degrees and take two more readings, four in all.

4. If the maker gives a limit for the difference in diameter between the two ends of the ferrule (taper), check that as well.

5. Record the readings: date, hose, fitting, die and measured diameter.

What tolerance should I expect?

The tolerance is also in the maker’s table and it differs by fitting. A reading outside the table value and tolerance is not acceptable. Look up each hose and fitting pair in its own table and do not carry one value over to all of them.

What if the size is out of range?

Reading above the table (under-crimp): check that the die and the fitting code are right and check the closing setting of the press.

Reading below the table (over-crimp): the die may be too small or the setting too far; the hose braid may be damaged, so do not use the assembly.

Every press and die set has manufacturing tolerances, so the real setting is found with a test crimp: crimp a new hose and fitting, measure, and correct the setting.

Do not put an assembly into use if it is out of size.

How often should I measure?

Your quality plan sets the frequency the application needs. In practice always measure when you start with a new hose, fitting or die, after you change a die, after you touch the press setting, and on the first part of every job. In series production, add regular sample checks to these.

What commonly spoils the measurement?

Jaws touching the ridges.

Reading at one point only; an out-of-round ferrule then goes unnoticed.

Dirty or worn jaws, or calipers that were not zeroed.

Comparing with another maker’s table.

How do I hit the crimp diameter on my press?

The maximum opening diameter and the main die length of the press decide whether a die can be used on it: the maximum opening diameter is 200 mm on the MT 30, 300 mm on the MT 35 and 400 mm on the MT 55; the main die length is 150 mm on the MT 35 and 200 mm on the MT 55. Send us your hose and fitting size and we will name the right die and press. We also make dies in the form and diameter you ask for.