The purpose of barbed wire is clear to keep people out, because we all known chained link fences are real easy to jump. My question is why do they use the typical chain link fence with barbed wire and not another type. I have seen fences with real small chain link, that you can barely get more then 2 fingers in let alone your foot. It seems to me these would be harder to climb if not impossible. I have jumped more then one barbed wire fence and its really not that hard. But if the chain link was small enough the barbed wire would not matter. Is it simply because cost? It seems the typicaly chain link fence is almost designed to be abled to be climbed easliy.
I would guess cost, and accidents. In my youth, the holes in the link were easy to climb. We’d have tried small link, too, and our parents may have sued the owned for broken fingers. 
I’m not sure of your question. Are you asking why they put barbed wire or Constantino (sp?) wire on the top of a chain link fence? For one, it looks intimidating. Secondly, I haven’t seen the real small chain link you speak of, but I assume it would be much thinner and easier to cut with a pair of dikes. I can easily see the smaller chains costing twice what the regular ones would cost (think ease of manufacture, in addition to numbers produced. Finally, I’m pretty sure I could scale an 8’ fence if it had something sturdy on the top I could grab on to. You’d have to make the small chain without barbed wire higher than the regular chain with.
It’s called concertina wire. Named that way because it looks like the slinky-like bellows of a concertina.
Funny story I one read about the stuff, which is also called razor wire. The original manufacturer had a devil of a time selling the product when it was first invented and marketed. People considered it just too dangerous and cruel, even if the intended “victim” was someone who was obviously up to no good.
Then they tried peddling it here in NYC just as crime began to spike in the 1960s or 1970s. New York landlords and storeowners had a lot less compassion then the rest of the U.S., apparently, because sales took off! The product’s popularity soon spread across the rest of the country.
It’s the same wire guage as the regular stuff, just closer together so you can’t get a toehold on it.
The downside to “climbproof” fencing is that it cuts down on visibility - from about a 45 degree angle, the stuff become opaque, making it difficult to monitor whatever might be happening on the other side.
That’s Concertina Wire.
I’m guessing that cost is the main motivator. The chain link fence + razor wire prevents most of the break-ins and has a relatively low cost. Smaller holed fencing would be more expensive since it has more metal, and presumably would require stronger posts to support the extra weight.
Interesting info, stuyguy, thanks!
Here’s what Wiki has to say, after I used the correct spelling to look for it!:
When specifying a security fence, there is generally a choice made; you can install a fence to meet a reasonable level of security, or you can install for high security.
An example: Most communities require that a swimming pool be surrounded by a fence that is a minimum of four feet high. That wouldn’t stop anyone reading this, but it will stop younger children from being attracted to the pool and falling in. On the municipal projects that I work on, we usually specify a six foot high chain link fence with barbed wire. It won’t stop a determined person, but it will make a sharp definition between someone who casually walked on the site, and someone who made an effort to breach a known boundary. I think of it as a reasonable approach that absolves the owner of liability should someone gain entrance.
I haven’t had that much experience with high security fencing, but one project I worked on many years ago (a gold processing facility) required two parallel 12 foot high fences with razor ribbon on top. The fences were far enough apart that it would force an intruder to climb two fences. Guards or dogs could patrol within. I think they may have adopted prison standards. The emphasis here was not on liability, but on securing the premises.
Chain link fence mesh is usually 2 inches across, but can be smaller. Obviously smaller mesh means more steel, so you pay the premium; that has a lot to do with considering this to deter climbers. The wire itself can be as small as 12 ga (wire size), or as large as 6 ga, but 9 ga is the norm. Normally, one side of the fabric has the wire ends sticking out (barbed selvage) and the other has them folded over (knuckled selvage). Ordinarily the knuckled side faces up (especially if there is barbed wire) and is tied to the top rail, and the barbed side faces down to discourage “moles”. Although, I’ve had fences where people burrowed a hole under the fence, pulled the fabric away from the posts, and crawled under.
Spme time ago I specified a fence around a ballfield in an area previously used by people to walk their dogs. Days after it was installed, someone had cut a door using bolt cutters. Gotta love East Boston! Chain link is only a deterrent, not an impenetrable barrier.
With municipal facilities in rural areas, the best solution and most economic solution that we have found is to install an 8 foot high fence (no barbed wire), but to take the top rail and move it to the bottom, and to have barbed selvages both sides. It helps to prevent the burrowing, and the fabric flops around giving the climber a bit of a “fun ride”.