I’ve recently removed a radiator and replaced it with a new one. To remove the old one I removed the TRV4 head and replaced it with a blue plastic screw-on cap to fully close the valve. Having just installed the new radiator I came to refit the TRV4 head and found the mating screw thread the wrong size. What? How could that be? So I removed the TRV4 head from another radiator and observed that the two valves look different, though they both had TRV4 heads. The first image is the one with the new radiator. The TRV4 head thread is bigger than that of the valve - what am I missing?