Review on Boost Performance with Standard Motor Products SK9 Fuel Injector! by Trevor French

This was listed as one for my Ford. When the injectors didn't fit back into the manifold I checked the old ones and these, and sure enough, the original had the smaller bottom ones (a different color too). This has been found to be the case for several Ford applications. Any parts store will try to sell you the same size o-rings for top and bottom, not offset as it should be. Also the dealer won't sell you smaller o-rings, just the whole injector. I had to drive across town to a fuel injection shop to get the correct underbody o-rings.