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A hydraulic hose crimp chart tells you exactly which die to use and what final crimp diameter to hit for each hose and fitting combination. Misread one cell, and you get a leak — or worse, a blow-off at 4,000 PSI. This guide walks through how to read die size tables without errors, with worked examples from real crimp specifications.
According to crimping theory, a proper crimp deforms the metal past its yield point to create a cold-weld bond. The ferrule compresses the hose reinforcement wire and inner tube into a gas-tight connection — no oxygen or moisture reaches the metal, preventing corrosion. But this only works when the final diameter matches the chart specification.
What Is a Hydraulic Hose Crimp Chart?
A crimp chart is a reference table supplied by fitting or machine manufacturers. It maps each hose size and fitting type to the correct die set number and target crimp diameter. Think of it as the recipe card for a safe hose assembly.
Every chart includes three core columns:
| Column | What It Tells You | Example |
|---|---|---|
| Hose Size (ID) | The inner diameter of the hose, usually in dash numbers (-4, -6, -8, etc.) or inches | -12 (3/4″) |
| Die Set Number | Which die to load into the crimper | P32/45 |
| Target Crimp Diameter | The final outer diameter after crimping, measured with a caliper | 31.62 mm ± 0.15 |
A crimp chart, you’re guessing. And in hydraulic systems, guesses cause crimp failures that can injure operators.
How to Read a Crimp Chart (Step-by-Step)
Step 1: Identify Your Hose Type
Check the hose layline — the text printed along the outer cover. It tells you the construction type (1SN, 2SN, 4SH, R12, etc.) and the nominal size. This matters because a -12 2-wire braid (DIN EN 853 2SN) and a -12 4-wire spiral (DIN EN 856 4SH) have different wall thicknesses and need different dies.
Step 2: Identify Your Fitting Series
Check the fitting body for a stamp or marking. Common series include one-piece, interlock, and reusable. The fitting series determines which row on the chart applies. Mixing up one-piece and interlock rows is the single most common chart reading error.
Step 3: Cross-Reference the Die Number
Find your hose size in the left column, then scan across to the column matching your fitting series. The cell gives you the die set number — for example, P16/19 or P32/34. Load that die into the hydraulic hose crimper.
Step 4: Note the Target Crimp Diameter
The chart gives a specific diameter in millimeters with a tolerance (e.g., 31.62 ± 0.15 mm). After crimping, measure the ferrule with a vernier caliper. If you’re outside the tolerance range, the assembly fails QC.
Step 5: Verify with the Die Number System
Most crimper dies are stamped with their number. Confirm the die in the machine matches what the chart says. A die stamped P32/34 is not the same as P32/39 — off-by-one errors are surprisingly common on busy shop floors.
Crimp Chart Example: 3 Common Hose Types
Here’s a simplified excerpt showing how the same machine handles different hose constructions. These are representative values — always use the manufacturer’s chart for your specific fitting.
| Hose Size | Construction | Fitting Type | Die Set | Target Ø (mm) | Tolerance |
|---|---|---|---|---|---|
| -6 (3/8″) | 1-wire braid (1SN) | One-piece | P16/16 | 17.30 | ± 0.10 |
| -8 (1/2″) | 2-wire braid (2SN) | One-piece | P16/19 | 20.75 | ± 0.12 |
| -12 (3/4″) | 4-wire spiral (4SH) | Interlock | P32/34 | 34.25 | ± 0.15 |
| -16 (1″) | 4-wire spiral (4SH) | One-piece | P32/45 | 46.10 | ± 0.18 |
| -20 (1-1/4″) | 6-wire spiral (R13) | Interlock | P32/57 | 59.60 | ± 0.20 |
Notice how the same -12 hose needs a different die and diameter depending on whether the fitting is one-piece or interlock. That’s why identifying the fitting series before crimping matters. For more on fitting types, see our guide to hydraulic hose crimp fittings.
Die Number vs Crimp Diameter: Why Both Matter
Some operators skip the die number and just crimp until they hit the target diameter. That works — until it doesn’t. Here’s why you need to check both:
Die number controls the crimp profile. Different dies produce different hexagon shapes. Even if the final diameter is correct, the wrong die can leave gaps between the die segments, creating uneven compression. The SAE J517 standard specifies that crimp profiles must produce uniform radial compression.
Target diameter confirms the result. The die gets you close. The caliper measurement confirms you nailed it. If the die is correct but the diameter is off, you know something else is wrong — hose wall thickness variation, wrong ferrule, or die wear.
A quality electric hydraulic hose crimper with CNC control can store these chart values and auto-stop at the target diameter. For manual machines, you’re relying on the operator reading the chart and caliper correctly.
Common Chart Reading Mistakes
After watching operators on hundreds of shop floors, here are the errors that show up most often:
| # | Mistake | What Happens | How to Prevent |
|---|---|---|---|
| 1 | Wrong hose construction row (e.g., reading 2SN data for a 4SH hose) | Undercrimp — ferrule slides off under pressure | Always check layline before opening the chart |
| 2 | Mixing metric and inch columns | Wrong die loaded — crimp diameter way off | Stick to one unit system. Most charts use mm |
| 3 | Ignoring the tolerance range | Borderline assemblies pass visual but leak | Measure with caliper, not by eye |
| 4 | Using the wrong chart revision | Fitting design changed, old chart gives wrong specs | Date-stamp your charts and replace when suppliers update |
| 5 | Not checking die stamp against chart | Wrong die loaded — visual similarity can fool you | Two-second check: read the stamp, confirm against chart |
One Reddit user reported using dies that were one size off because the die markings were worn: “The dies are probably for thicker connectors and lugs, but those are hard to find online.” Worn stamps on dies cause real problems. If you can’t read the die number, replace it. A portable crimper with well-maintained dies always outperforms a heavy duty machine with worn ones.
Quick Reference: Crimp Tolerance by Hose Type
Tighter tolerances are required for higher-pressure hoses. Industry standard from crimp specification references is ±0.05 mm for standard applications and ±0.03 mm for safety-critical assemblies (brake lines, steering). Here’s a general guideline by hose construction:
| Hose Construction | Typical Working Pressure | Industry Standard Tolerance |
|---|---|---|
| 1-wire braid (1SN/1SC) | Up to 3,000 PSI | ± 0.10 mm |
| 2-wire braid (2SN/2SC) | Up to 5,000 PSI | ± 0.08 mm |
| 4-wire spiral (4SH/4SP) | Up to 6,500 PSI | ± 0.05 mm |
| 6-wire spiral (R12/R13) | Up to 5,000 PSI (larger ID) | ± 0.05 mm |
| Safety-critical (brake/steering) | Varies | ± 0.03 mm |
High-end CNC crimpers like the TRC P32D achieve ±0.02 mm precision — well within all tolerance bands. Manual crimpers typically operate at ±0.10 to ±0.15 mm, sufficient for low-pressure applications but marginal for spiral hose.
These tolerances come from the ISO 8434 and DIN EN standards. Your fitting manufacturer’s chart may specify tighter ranges. When in doubt, follow the tighter spec. For workshops running high-volume production, a heavy duty hydraulic crimper provides the tonnage consistency needed to stay within tolerance on larger bore hoses.
Tools You Need Besides the Chart
A crimp specification sheet from your fitting supplier is the final authority. The chart in this article is a representative example — always defer to the manufacturer’s data for your specific parts.
- Digital caliper (±0.01 mm) — For measuring crimp diameter. A hydraulic crimper operator without a caliper is flying blind.
- Die reference sheet — A laminated card showing all die numbers with their hose range. Hang it next to the machine.
- 67# anti-wear hydraulic oil — The chart assumes proper machine lubrication. Dirty or wrong oil changes the effective crimp force.
- Ferrule and fitting samples — Keep one known-good assembly on the bench for visual comparison.
For shops running a manual hydraulic hose crimper, consider upgrading to a CNC model like the TRC P32D that stores chart data electronically. It eliminates the risk of reading the wrong row. See our crimping machine upgrade guide for more on when CNC pays for itself.
Need the Right Dies for Your Hose Assemblies?
TRCrimp supplies die sets for all 9 series with factory-matched crimp charts. Every die ships with a tested specification sheet.
FAQ
What does a hydraulic hose crimp chart show?
It maps each combination of hose size, hose construction, and fitting type to the correct die set number and target crimp diameter. You use it to select the right die and verify the finished crimp with a caliper.
Can I use the same chart for different crimper brands?
Generally no. Die numbering systems differ between manufacturers. A P32/34 die from TRC may not match a P32/34 from another brand. Always use the chart specific to your crimper and fitting supplier.
What happens if my crimp diameter is 0.3 mm over the chart spec?
An overcrimp of 0.3 mm can restrict the hose inner diameter, reduce flow, and create a stress point. It can also crack the ferrule. Reject the assembly and re-check your die selection.
Where do I find the crimp chart for my fittings?
Your fitting supplier should provide a chart with every order. If they don’t, ask for it — it’s a safety document. Some manufacturers publish charts online or provide PDF downloads.
Do I need a different chart for skived vs unskived hoses?
Yes. Skiving removes the outer cover, which changes the ferrule-to-hose fit. The target crimp diameter is typically smaller for skived assemblies. Check the chart’s skived/unskived columns.
How often should crimp charts be updated?
Whenever your fitting supplier revises their product design. Keep the chart revision date visible and request updates at least annually. A bench-mounted crimper should have the current chart posted within arm’s reach.
Can I calculate crimp diameter without a chart?
Not reliably. Crimp diameter depends on ferrule wall thickness, hose construction, fitting profile, and die geometry. The chart is the product of factory testing — there’s no safe shortcut.
What’s the difference between crimp diameter and die opening?
Die opening is the gap between die faces before crimping. Crimp diameter is the final measured diameter of the ferrule after crimping. They’re related but not the same value.
