Yes that's right. I'm not shure what 50/40's are. Are they the rockwool cubes for starting seeds I saw with the system. If the rapid rooter is the cloning hydro setup then yes.. the rapid rooter plugs are for starting from seed you need some thing that will not wash down into hydro system when put into place . That's why we use rockwool and you have to be careful because rockwool can cause stem rot if it stays too wet later.