The stock lead screw nut has threads in the bolt hole. The replacement lead screw nut does not.
You can use the stock bolts, but will need to add 2 M3 Nylock nuts to secure it.
You will need to remove the 2 split washers used in the stock installation in order for the stock bolts to be long enough to be secured by the Nylock nuts.
The new lead screw will need to be lubricated before it can be used. In this case white lithium grease is used since it is a good medium weight, does not drip like light oil, and it will not dry out.
I like to place a few small blobs of the grease along the length of the lead screw and then jog the axis up and down to work it in.
The small bead of grease that accumulates at the nut will act as a self lubricating seal during normal use.
Not that the filament path goes right next to the lead screw. If you're worried about getting grease on the filament consider printing a filament guide such as this one:
Ender 3 Filament Guide
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