you have to do a couple things, scribe a STRAIGHT line down the center of it so you can get it straight after you cut it. Then find some tubing that fits inside snuggly. than cut a piece of tubing the same size as the stem and put a good bevel on each end. insert and tack weld the inner piece (it should stick in 3 or 4 inchs on each end), slide the spacer you made over that then the other end of the stem. check alignment with you scribe mark, tack weld, double check alignment then weld it getting penetration of the stem, spacer and sleeve. this is why you made the bevels.