The two parts SHOULD go together only in two different positions, either one of which is satisfactory. It is important (from a constant speed standpoint) that the fixed yokes at the end of each piece be in the same plane. You should not be able to insert the two pieces such that they are 90 deg out...180 out, OK...but not 90. The PTO shafting that I have is that way but some may not be. I have seen some that have rectangular shafting such that they can only be assembled in the correct phase. If yours is square, like mine, see if there is a nub or something on one side of the male piece that fits into a corresponding internal slot in the female piece. I had a problem with mine once in getting the two to mesh all the way by hand. It was due to rust buildup on both pieces...it is a fairly snug fit. Of course it COULD have been bent slightly when it came apart. It wouldn't take much to prevent the two pieces from sliding together freely. You probably would not notice it by just looking.