Hexagonal Head - Myson. Genuine Myson adapter. 28mm to 30mm Head Adaptor for Lowenergie TRV 2-Way Thermostatic Radiator Valve. 28mm to 30mm Head Adaptor for TRV 2-Way Thermostatic Radiator Valve. The male thread on the top of the adaptor is M30 (30mm) and the female thread on the bottom is M28 (28mm).