Need help with prop? Something's not right

Hello everyone! I'm new to this boat scene and could use some help. I have a bass tracker tournament 1800fs I just picked up. It has a Johnson GT 150 pro series motor. When I bought the boat it had a solas 19 pitch prop on it and it was beat up bad so I went to the boat shop and thye insisted to get a 17 pitch. So I bought one new Solas 17 pitch. I get home and pull the old one off and the old one has a small nut to tighten prop down on the shaft but behind that nut on the prop is a bigger nut. My new one isn't like this. When I put the new prop on the splines are showing past the end of the prop which won't allow the nut to tight the prop down. I'm trying
to up load pics but not working. If anyone could help I would really appreciate it.

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No the thrust bearing was still on the shaft. And also I'm at high elevation in colorado mountains and the boat shop said that a 19 pitch would be to much. So he said 17 pitch would be better. The boat is from Texas so I don't know how it reacts to this elevation. The boat is 18 ft

My old prop didn't have that thick washer behind the nut. I'm thinking that's exactly what I need. Thank you

That's weird how different that prop is and same manufacture. Thank you for the help! It's a TJ150SLCEM.

Yes I'm sure. Because when I pulled it apart there was a nylon/ plastic lock washer between the prop and the nut. When putting the new prop on that washer isn't thick enough, the nut maxes out to the splines and the new prop won't tighten down. From the info you have me and othere motors I've researched they use that brass thick washer. So I'm gonna get one and try it out