I have a 1996 Chevrolet Cavalier z24 and this engine oil filler cap doesn't fit quite right. When I first received it and went to install it, it would tighten down about two turns and then stop way before reaching the o-ring gasket like its supposed to. I went ahead and drove to work (about 55 miles from my house) and by the time a got to work the cap had started loosening up and I had to re-tighten it again. This went on for about a week until I was able to tighten it down all the way to the o-ring gasket and snug it tight like its supposed to be.
I think that the heat generated by the engine allowed the plastic/polyurethane threads of the new engine oil filler cap to gradually conform to the threads of the engine oil filler port on the engine itself.
I hope this review is somewhat helpful to someone who might be thinking about buying one.