That 1/4" cap / plugs are not my favorite and I don't currently own any engines that use it. A year or so ago, a friend was at my house and I helped him install a new Evolution 10 in his airplane. I had a heck of a time teaching him how to install and remove that cap! He was afraid to push hard enough to allow it to rotate so it would lock. I thought he was good to go until some time later we met at the field. On the first start, the cap fell off the plug and you guessed it ..... it wasn't on far enough and locked.