2004+ Ranger Locking Gas Cap
When I sold my 2003 Ranger I saved the locking gas cap. Too bad it didn't fit my 2004 - Ford had changed the gas cap design.
I asked the dealer parts department if they made a locking cap for 2004 Rangers, and was told several times that none were available. Recently I heard that the locking cap for the 2005+ Mustang would also fit 2004+ Rangers (along with several newer Ford cars and trucks).
The cap number is FC-1016 and the full part number is 6L3Z-9030-AA.
I picked one up, and it fits and works perfectly. It came with a plastic push-type rivet in the attached tether. I removed the rivet and fastened it with one of the sheet metal screws.
List price is about $36 - I paid $26 at a Ford dealer. Dealer prices vary and online Ford parts sites sell it for less, so shop around.
Since the gas cap is part of the emission control system, it's best not to use a cheaper cap to save a couple of bucks. This is the one to get.