As earlier mentioned, we sail an Inter 18. The sails from this boat are not in an excellent state anymore (still the originals) Therefore we're looking for a new set.
Now it comes to my attention that some suppliers are offering "F18" sails, and others offer especially for the Inter 18.

Can anybody explain if these are the same? If we see an ad for F18 sails, are they suitable for our boat?

Sails are cut to the mast, every good F18 sail maker knows this. Does your boat have a carbon rig or aluminum rig? That will make a big difference.

Ohh, didnt know that. It's aluminium

I was just looking at young used ones and new onces based on price lists from some well known makers.

If you aren't racing hardcore then any set of F18 sails should work on your platform, but don't hold me to that.

No not all F18 sails are the same. The Nacra F18 mast has changed many times and you need to fit a sail to your mast. Contact the sail manufacture and ask them what they have or can make for your boat.

Or you can go with another sail loft. bring your cat there, and rig it so they can see and measure your luff track.