The diameter is 4mm for Mercedes-Benz Air Ride Suspension Air Line Hose -5 m

Condition:New|Adjustable:Yes|Brand:Unbranded|Country/Region of Manufacture:China|Features:Easy to Replace|Fit for:for Mercedes Benz |Fitment Type:Direct Replacement|Gas Charged Shock:Yes|Items Included:Air Ride Suspension Air Line Hose|Manufacturer Part Number:Does Not Apply|Manufacturer Warranty:1 Year|Number in Pack:1|OE/ Part Number:Air, Connector, for Mercedes-Benz S-Class W220 2000-2006, Line, for Mercedes , Straight Union, Suspension|Type:Air Suspension Compressor Kit