I have 2 of the Baxter Threading Jigs and I can use them on all of my lathes (Victor made me another piece for my BTM-17 so that I can use it on my Powermatic) I have yet to find a wood that I cannot thread successfully. I have 8, 10, 12, 16 and 24 tpi heads (the 24 tpi is not made anymore and I really don't know why I bought it so long ago). I can thread 1/4" to 5" diameters. Changing the heads is super easy and manufacturing is done so well everything always lines up perfectly. I have a piece of Iron wood that is so hard that even a file has trouble getting shavings off of it. I tried turning it with a Oneway chuck and the Oneway screw and it broke the screw trying to put a tenon on it. It is harder than concrete. It took a large vise a drill and an easy out to get that broken screw out. Maybe fresh cut Iron wood would work but this piece is a conversation piece.