The Caleffi 681503A is a universal PEX fitting, 3/8 in nominal PEX to a 3/4 in straight-thread female nut, chrome plated. It connects ASTM F876 single layer PEX to the 3/4 in male conical pipe connection on the Caleffi 301 series panel radiator valves.
Best for connecting 3/8 in nominal PEX to a Caleffi 301 series panel radiator valve.
Specifications from Caleffi datasheet 01036/23 NA, 681 series universal PEX fittings. Reviewed August 2026.
Key Features
Universal ASTM F876 Compatibility
The 681 series is compatible with any ASTM F876 single layer PEX, so it is not tied to one pipe brand.
3/4 in Straight-Thread Female Nut
Mates to the 3/4 in male conical pipe connection on the Caleffi 301 series panel radiator valves, the family this fitting is documented against.
Rated to 150 psi
Maximum working pressure 150 psi. Working temperature for ASTM F876 PEX piping is -41 to 180°F.
Chrome Plated
Chrome-plated finish matching the exposed valve bodies, suitable for visible radiator connections.
Technical Specifications
| Product Type | Fitting |
| Series | 681 Series |
| Connection type | PEX |
| Pipe connection | 3/8 in nominal PEX |
| Valve connection | 3/4 in straight-thread female nut |
| Pipe standard | ASTM F876 single layer PEX |
| Finish | Chrome plated |
| Max. working pressure | 150 psi |
| Working temperature for ASTM F876 PEX piping | -41 to 180°F |
| Documented valve family | Caleffi 301 series panel radiator valves |
Documentation
Related Products
- Caleffi 437516 : Compression Fitting 1/2" Copper
- Caleffi NA10262 : Adapter Kit to 1/2" Sweat
- Caleffi NA10313 : Adapter Kit to 1/2" Male NPT
- Caleffi 387127 : Universal Radiator Tool
Frequently Asked Questions
What is the Caleffi 681503A?
A universal PEX fitting that connects 3/8 in nominal PEX to a Caleffi radiator valve. It has a 3/8 in PEX end and a 3/4 in straight-thread female nut.
What PEX does the Caleffi 681503A work with?
Any ASTM F876 single layer PEX at 3/8 in nominal. For multilayer PEX-AL-PEX use the Caleffi 682 series instead.
What are the pressure and temperature limits?
Maximum working pressure is 150 psi. Working temperature for ASTM F876 PEX piping is -41 to 180°F.
Which valves does the Caleffi 681503A fit?
Caleffi 301 series panel radiator valves, the family this fitting is documented against in datasheet 01036/23 NA. It uses the 3/4 in male conical pipe connection.
- Product Type:
- Fitting
- Product Family:
- Fittings and Accessories
- Series:
- 681 Series
- Connection Type:
- PEX
- Connection Size:
- 3/8 in
- Pipe Standard:
- ASTM F876 Single Layer PEX
- Fits Series:
- 301 Series
- Max Operating Pressure:
- 150 psi (10 bar)
- Max Medium Temperature:
- 180 deg F
