Domestic to International Flight bag transfer. Delta to Neos

How does 2 check in bags work from Delta to Neos?

Neos is a budget carrier and not an interlining or code share partner of Delta so this sounds very much like two separate tickets or "self connection" (which is a terrible idea). In this case you check-in in Cleveland with Delta. On arrival you pick up your bags at the luggage carousel. Then you go to the Neos check in counter in New York and check in for your flight to Milano and drop of the bags again. Make sure you have plenty of time for this. Personally I would not do a self connection with less than 4 hours.

What is the weight limit and what is the cost over 50 lbs?

The allowance depends a lot on the type of ticket you bought and it should say so on the ticket. It varies anywhere from nothing to 2 large bags. Keep in mind that you have to pay separately for Delta and Neos, so this is going to cost you dearly if you exceed your allowance. Going over 50lbs will cost you even more. Delta alone charges you $100 for 50lbs-70lbs and $200 for 70lbs-100lbs.

For Neos see here:

• https://us.neosair.com/en/before_the_flight/baggages/hold_baggage

For Delta

• https://www.delta.com/us/en/baggage/overview
• https://www.delta.com/us/en/baggage/checked-baggage/excess-overweight-baggage

Do I have to go through security again?

yes.

Tip: check connection rules and baggage allowances BEFORE you buy a ticket. If you bought the cheapest available tickets the baggage fees can easily double the total cost.

The answers to all of your questions is dependent on your ticket.

• What is the weight limit and what is the cost over 50 lbs?
  This very likely varies from class to class, whether it is business class, premium economy, economy etc. You should be able to look it up on your reservation online, or based on ticket class, like this one for delta.

• Do I have to go through security again?
  JFK has multiple terminals. Not all terminals are connected air side. Based on the airport's website, Delta seems to operate out of Terminal 2 or 4. Neos operates in Terminal 1. It looks like you have to do security again. Note these things can change sometimes. But whether you have to check bags out and then in is going to be dependent on if both flights are part of a single ticket, or two tickets. If you bought a single ticket with two legs, it is very likely that your bags will be checked in through to Milan. If you bought the tickets separately, or if you bought it from one of those online sites which advertise very cheap tickets that do this, then it is unlikely that they will be checked in through. In some cases, even if they are two tickets, you may be able to request to check in through the final destination.