I have a Shindaiwa T231 and I bought a speed feed 450 replacement head. However there is a adapter bolt that I cannot remove from the gear casing. You can see it here as piece #1 http://www.shindaiwa.com/nam/en/_docs/trimmerheadguide.pdf right below the bolt is the the collar on the gear shaft seen here as #11 http://www.shindaiwa.com/nam/en/_docs/ipls/trimmers/t231_t231b.pdf The collar and bolt spin independently and I can't see a way to lock the gear case to unscrew the bolts. Honestly this is maddening. Can someone please help me out here?