This is not a 5-star review because the original order did not arrive as scheduled, apparently lost somewhere in transit by the USPS. And there were a few problems with the door itself, noted below. It is a 4-star review because, when I contacted Seacorals to report that I still had not received the shipment several days after it was supposed to arrive (and was not able to find out anything about its current whereabouts using the tracking number supplied by the USPS), they promptly sent me a new door and expressed considerable concern over the shipping failure. Also, the problems with the door did not prove to be serious.The cat door itself appears to be of good quality, and is not difficult to install, though installation in a 1.75 inch thick solid-core door between our house and garage presented some challenges.First, the liner that fits inside the cut-out is not nearly long enough to cover the entire thickness of a door this wide, leaving an unappealing brown strip visible through the middle of the opening. I solved that problem simply by lining the cut-out with white plastic duct tape. This matched the white paint of the door and the white plastic of the cat door liner closely enough to be unnoticeable, at least to a casual inspection.Second, although the cat door apparently is supposed to assemble using 8 short #6 screws to independently attach each side of the frame to opposite sides of the door (4 screws per side), I didn't like this "non-aligning" assembly feature. So I decided to get 4 long screws to "self-align" the two sides, cinching them together by passing the screws through the room door around the cut-out. For my 1.75" door, my first guess was that 2.0" #6 screws (the longest #6 screws I could find at the local hardware), would do the trick, but these proved a bit too short to go through the door when widened by the 2 frames on each side of it. I then moved on to 2.5" #8 screws, which were long enough. The extra thickness of the #8 screws was not a problem (I just drilled the pilot holes through the door a little bigger). So that was all good.The installation bonus was that, to position the cat door low enough for the cats to use, I had to install it across 2 raised panels of the room door. This meant there was a "V"-shaped depression in the middle of the opening on each side that, when I first cut it, I thought I would have to fill in with some type of sealer under the frames, to make the opening air-tight. However, when the frames were fitted to the opening--although the inside liner was not long enough to reach all the way through the door--it did prove long enough to completely cover these depressions, providing a good tight fitting seal all the way around the opening on each side, with no additional effort. (If you don't want to settle for the pretty good natural seal provided by the frame liners, you could easily caulk around the outside of the frames to ensure a perfect seal.)As for the cat door itself, once installed, it seems perfectly functional. Although our 2 cats are both still kittens, the door appears to be the perfect "Goldilocks" size -- not too big, but not too small either for an adult cat, just right. Due to the magnetic closure feature, the flap operation of this door is stiffer than the free-swinging flaps I've had in the past -- the flap stops abruptly in the down position and has to be "broken" free when opened -- but that fact didn't seem to bother either kitten, both of whom learned to pass through it freely in less than a day.The 4-way closure feature is logically complete, covering all possibilities (which I appreciate abstractly, as a former teacher of logic), though we only need 3 of the 4 settings. (Open both ways, so the cats can pass back and forth at will; open out only, so the cats can't come back in the house when they are banished to the garage for some reason, e.g., cat-allergic guests; & open in only, so the cats can't go out into the garage when some activity is in process better done without a curious cat in attendance, e.g., working with power tools. I guess the fourth setting, open neither way, might be useful if you had two incompatible sets of animals needing temporary separation.)My only small concern is the plastic locking tab has to be pushed up to slide it back and forth, and I don't know how durable this plastic tab will prove to be over time in daily use (I've had a lot of plastic tabs break off over the years). But, so far, so good.Installed the cat door on a 2 inch exterior insulated garage door. Overall the installation went pretty well (make sure the sabre saw blade is long enough on the up stroke otherwise you will get a lot of bouncing). The previous cat door we had allowed water to infiltrate the door and it eventually rusted out. This door has a better design and has a ridge line across most (but not all) of the bottom so most water should run out, and not in. Our previous cat (a smart Calico) saw me push the flap open once and instantly knew how to use it. Our Ferrell cat we have adopted will walk through the opening if the door is propped open, but so far will not push it open, so she will need some training, The attached picture shows the door propped open with some painters tape. I also made a U frame around the cat door with some 1 inch aluminum channel from one of the big box stores. When we want to lock the cat in the garage at night, we slide a piece of half inch board in the U channel to lock her in. The board also has an aluminum L handle at the top to make lifting it easy. Works really well and better than having to flip the red and green locks. We only use those when we want an in-only door. for when we are away, I'm also thinking about making a remotely lockable flap that would slide into the U frame and be activated with a Kasa HS103 remote control device, a 12V wall wart supply, and a 12V actuator but also need to fix a security camera on the door so I can monitor what is happening in the garage. What we won't do for out pets.Many years I had PetSafe cat door installed for door from garage to house (it was replaced twice due to wear out). The problem was that my door is hollow and slightly less than 2" and the look from garage was to say mildly 'ugly'. Then my cats learnt how to open the lock on this cat door - they claw it until it will slide open and recently they just ripped the slider off completely.So in search for a new door replacement I found this one with door liner (at first I found liner and was thinking to buy liner and PetSafe door again - because the hole already there). I was hesitant because given measurements for 'Cat Mate 4 Way Locking Cat Flap with Door Liner' were slightly larger than PetSafe 2-way lock door, but decided to risk and mentally was preparing myself to sawing project for the larger hole.To my surprise (and joy) this door fit exactly to existing hole from PetSafe. Installation was easy and the door liner looks amazing. The other good feature that this door has dark gray transparent flap and cats can see through it if somebody is waiting to jump on them from the other side. Not all cats accepted it equally easy - some were very cautious to go through the new door, but after couple day they using it without any problems.In addition, I have huge 18.4 pounds cat - he can go through this door also without problems - just slowly sliding through it.Locking mechanism works great, but right now it is difficult to say how long it will hold (the locks are from garage side).Overall I am very happy and very satisfied with quality and features of this product.Last time I purchased this item was in 2013, and it is still going strong.I needed another cat door for another part of my house, so needless to say I am a returning customer. This cat door has weathered 3 cats for 9 years with no issues at all. I have a 15 pound cat that has no issues getting through.The cat wouldn't tell me what he thinks about this so I've tried to guess. Generally he looks at everything with a huge amount of disdain: his food, the kids, the TV...so I've come to the conclusion that this cat flap is equally as low down in his estimations. But he is a cat after all and I quite like this cat flap so it gets 5 stars. You're welcome.After 4 weeks ( yes 4 ....they are thick what can I say) my cats have finally got the hang of using this. So much so they go in and out of it when the door is open. A friend put it in for me through the bottom panel of a double glazed door. You will need a jig saw with a metal bit as the door has metal on both sides under the plastic coating on the panel but it was easy enough t to fit.Cons..every cat in the area comes in to chow down on any food still in their bowls. In fact they got the hang of it before mine did. We have also had a fox cub, a pigeon and a small dog. That could be solved with a magnetic flap and collars on the cats but mine lose collars so I didn't buy that option. Also, of course, they bring their "road kill" in via it as offerings.Pros....they can get in and out without me constantly going to the door. We have one called Brexit cos he can't make up his mine if he wants to be in or out. I no longer have to stand there waiting for him to decide. I don't have to worry if am out and it rains cos they can come straight in. If next door's dog chases them they can escape etc. My 20 year old cat can get in and out via it too.Edited. I bought this flap again as the locks got broken and we have a kitten I don't want to let out yet. I locked it so my older cats could all get back in but not out. However any cat with any sense can work out how to get around the locking system. My one eyed cat just smacks the flap hard until it moves towards him then hooks his paw under it and off out he goes. One of my other cats watched how the slider lock works and just opens it now with his paw. So the locks are a waste of time in my house anyway.Purchased this product as we have a large cat, my wife and I were however worried it wouldn't fit through before receiving the product. However the dimensions and size guide was right, and our Siberian fits through no problem.Our upvc door is required us to use the tunnel which worked great. I had never cut a hole in our back door or installed a cat flap, but the instructions were easy to follow and it came with a handy template to put on the door and draw your cutting area. Fairly simple (but slightly time consuming as your have to cut a big whole in your door) installation.A nice neat finish once installed, no sharp bits that could hurt the cat, and seems nice a sturdy but easy enough for the cat to get in and out.The magnet that holds the door in place is a great addition, and the brushes round the edge stops and draft coming in. The locks that can stop the cat going in/out or both are simple and effective. Though do seem like they could break eventually so don't force them across.Simple packing, fairly compact that can be recycled. Great product on the whole at a great price!This is an outstanding cat flap. I purchased in 2014 and it's still working flawlessly. And I have 3 cats whom often charge through it. But it's so robust, it's incredible. The 4 way slide tabs at the bottom are still working great. Honestly, if you want a non fuss simple 4 way cat flap. Then this is the boy for you. The screen door being clear is something my cats love. They often simply sit and stare through it to the outside word. Plus even after 3 years the clear screen door remains unscratched and perfectly clear. It's a perfect size too. Suitable for the smallest to the largest cat. My largest cat is at 6kg and she fits through it lovely. (Btw I do have my 6kg cat on a strict diet at moment as she needs to be around the 4kg mark) To fit, it's a simple job, it's adjustments allows for thin or quite thick PVC Doors. My door is at say 12cm. And that's aboutit really. An exceptional piece of kit, should you not require a more advanced feature such as ID Chip recognition, or time schedule operation. Very pleased with this. Nearly 4 years and still working a dream.Bought this for my one year old cat Joe who was destroying my house and my dog so decided to let him be an outdoor cat ,got a joiner to install it in my pvc door and after a few days of pushing Joe through the hatch he got the hang of it and now is a very happy boy he no longer destroys my home and less plotting of the death of my dog absolutely brilliant .