Hello. I'm trying to adjust the handlebars on this Carnielli stem, and I'm unable to loosen (or for that matter) tighten the stem bolt. There is nothing on the front of the bolt to react the torque applied to the nut, such that the bolt just spins around? Searching the threads I saw a Cinelli stem with a keyed or serrated bolt. Is that what is used in this stem? Or am I missing something obvious (I don't know why the bolt head has a flat on one side)? Thanks