whad they do???...change them on me?? OK Bob...I bit. I went and checked all our 2014 and 2015 FR units on the lot. They and the 2014 Tioga all have the 4" bumper. So... you need a 4" like Bob says. Thank You Bob for pointing that out...your handy to have around here unlike some of us...
edit...you cant see the slot in the dowel very well. it just slides over the bumper and then the set screw tightens.