Hoffman Model 508 Part No. 401475, 1/8" Straight Steam Convector Air Valve (non-vacuum) - Disc-type vent - Built-in Check Valve - For automatic venting of convectors and radiators - Can be disassembled to clean without removing from line - 1/8" NPT straight shank - Maximum steam pressure of 15 psig (1.0 bar), Hoffman 508 radiator water vent valve, 1/8"NPT male straight shank, 50lb maximum, for automatic or manual venting of radiators, disc type vent with built in check valve.