The name Hassler was changed to Haszler by Frederick Haszler Sr. for the purpose of keeping  the mail separated from another Fred Hassler.  Fred changed his last name from Hassler to Haszler in about 1909.  There were two Fred Hasslers on the rural Peru mail route.  The other Fred Hassler was in bussiness and Frederick got tired of having the mail mixed up, so he changed the spelling.