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Note: When you Order a pair of Locking Fuel Caps, they will be Keyed Alike (use the same key).
Cap Assembly Aluminum 4.0" - 8 NPSM / LOCKING (ID of Cap 4.35")
The 4” Locking fuel caps is a non-vehicle specific fuel tank cap that will fit almost any of the 4" threaded fuel tank necks. This fuel tank cap is stamped with "DIESEL ONLY KEEP CLEAN" on the top.
The 12.00" Chain & 8.35" Bail keeps your fuel cap from getting lost while your fueling.
Note: Always measure the inside diameter (ID) of Fuel Cap for a more positive Identification if there is any question as to which Cap to use. Should the Cap not be available - measure the outside diameter (OD) of the Fill Tank Neck to determine inside Diameter (ID) of Cap.
Always make sure and if the Tank is either Vented or non-Vented in order to spec correct Vented or Non-Vented Cap. (note: a Vented Cap is made to work with a non-Vented Tank; it is also safe to use on a Diesel Fuel Tank that is already Vented) a non-Vented Tank Must have a Vented Cap to operate properly.
The inside diameter (ID) of Caps used with Low-Sulfur labeled Diesel Fuel Tanks are smaller and have different treads than Caps used with Diesel Fuel Tanks that have no Low Sulfur Label. (See the Volvo Description on the above PDF File as an example)
All Caps are Threaded Female style. (except the Peterbilt Lever Style and Freightliner Cam-Cap Style) Some Older Fuel Tank fill necks (pre 2000) may have a different size and thread than current Tanks.
Though Steel Tanks are not as common in the HD Truck Industry as Aluminum, it is recommended to clarify whether the tank is Aluminum or Steel.
NPSM (National Pipe Straight Medium) Threaded Caps will not fit NPSL (National Pipe Straight Loose) or NPT Fill Neck Threads. However, NPSL will fit NPSM threaded Fill Necks.