Product Details
The Flexfab 5521-125 is a green cover/red liner silicone, 1-ply nylon hose engineered for demanding engine environments. It resists hardening, cracking, cold leaks, aging, and many chemicals, making it a durable, long-lasting solution for diesel, automotive, marine, agricultural, and industrial cooling systems. The recommended Flexfab clamp for this size is shown in the chart below.
Performance & Construction
| Construction | Green cover/red liner silicone, 1-ply nylon |
| Inside Diameter | 1.25″ (32 mm) |
| Outside Diameter | 1.64″ (42 mm) |
| Actual Burst Pressure | 200 PSI |
| Working Pressure | ~67 PSI (1/3 of burst) |
| Temperature Range | -65F to +350F |
| Wall Thickness | .170″/.220″ |
| Standards | SAE J20 R3 Class A; TMC RP303B Cl I Gr II |
| Origin | Made in USA |
Why this hose
- Green cover/red liner silicone, 1-ply nylon — durable construction engineered for demanding cooling-system service.
- -65F to +350F range — stays flexible in cold and handles under-hood heat without hardening or cracking.
- Resists hardening, cracking, cold leaks, aging, and many chemicals — long service life where ordinary rubber fails.
- Meets SAE J20 R3 Class A; TMC RP303B Cl I Gr II — engineered to recognized heavy-duty hose standards.
Frequently asked questions
Is this hose fuel-rated?
No. Silicone heater hose is for coolant, radiator, and heater applications — it is not fuel-resistant. Do not use for fuel or oil lines.
What clamp does it take?
Use the Flexfab 2582‑0020 clamp, sized to this hose’s outside diameter. Two clamps per connection is standard practice.
Flexfab 5521 Series — Complete Size & Clamp Chart
Every size in the series. Click a part number to open that product. The clamp column shows the Flexfab clamp(s) that fit each hose OD.
| Part | ID (in) |
ID (mm) |
OD (in) |
OD (mm) |
Actual Burst |
SAE | TMC | Weight (lb/ft) |
Matching Clamp |
|---|---|---|---|---|---|---|---|---|---|
| 5521‑025X25 5521‑025X50 5521‑025X800 |
0.25″ | 6 | 0.64″ | 16 | 475 PSI | 475 | 125 | 0.121 | 2582‑0006 |
| 5521‑031X25 5521‑031X600 |
0.31″ | 8 | 0.70″ | 18 | 475 PSI | 475 | 125 | 0.151 | 2582‑0006 |
| 5521‑038X25 5521‑038X50 5521‑038X500 |
0.38″ | 10 | 0.77″ | 20 | 475 PSI | 475 | 125 | 0.181 | 2582‑0006 |
| 5521‑050X25 5521‑050X50 5521‑050X500 |
0.50″ | 13 | 0.89″ | 23 | 425 PSI | 425 | 125 | 0.226 | 2582‑0006 |
| 5521‑062X25 5521‑062X50 5521‑062X400 |
0.63″ | 16 | 1.02″ | 26 | 375 PSI | 375 | 125 | 0.258 | 2582‑0010 |
| 5521‑075X25 5521‑075X50 5521‑075X300 |
0.75″ | 19 | 1.14″ | 29 | 325 PSI | 325 | 125 | 0.301 | 2582‑0012 |
| 5521‑087X25 5521‑087X50 5521‑087X150 |
0.88″ | 22 | 1.27″ | 32 | 300 PSI | 300 | 125 | 0.346 | 2582‑0012 |
| 5521‑100X25 5521‑100X50 5521‑100X200 |
1.00″ | 25 | 1.39″ | 35 | 300 PSI | 300 | 125 | 0.391 | 2582‑0016 |
| 5521‑125X25 5521‑125X50 5521‑125X150 |
1.25″ | 32 | 1.64″ | 42 | 200 PSI | 275 | 125 | 0.491 | 2582‑0020 |
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