From 7990 Thermostatic Valve Pay & Collect Submit your order now and collect your items at your local Biltema store in 2 hours! This is how Pay & Collect work For regulating flow in radiator systems. Fits most thermostat dials with M28 connections. Connection to radiators, external thread M26 x 1.5. Pipe connection internal thread 3/8” (R10) or ½” (R15).