New steering coupler doesn't fit!

Pettybluedart

I'm pretty sure that I have the new coupler positioned the same as the old one. I transferred a mark to the new coupler just as it was marked on the old one so that their position are the same when trying to slide on. I noticed that on the old coupler and the new coupler there is a notch machined into the bottom on both couplers at the same spot. I looked at the inner threads on the bottom of the couplers and they don't look any different and also doesnt look like there is an area where some threads are missing. Are some couplers machined different? I'm at a loss?