GARDEN HOSE NOZZLES
Pistol Grip Garden Hose Nozzle

Here we're talking about pistol-grip nozzles such as the one shown above.  If you are shopping for such a nozzle, there is one very important feature for you to look for -- and it isn't even visible.  It's the spring inside: it should be stainless steel.

Here's why:  That spring is immersed in water.  Most of these nozzles use a plain steel spring, which rusts.  Rusting removes part of the metal,
gradually making the spring thinner and weaker.  Eventually it gets weak enough that when you release the trigger, it fails to shut off the water.  Then you get really pissed off at the nozzle and slam it against the concrete driveway, the usual failure mode of such nozzles.

But if you can't see it, how do you know the spring is made of stainless steel?  Simple:  It says so right on the package.  If it doesn't say it has a stainless steel spring right on the package, trust me, it doesn't have one!  I can report that Ace Hardware sells pistol grip nozzles with stainless steel springs; in fact, they have a selection of several different models.

The stainless steel spring is far and away the most important feature to look for, but I can also elaborate on other materials and features.  Pistol grip nozzles are typically made of either metal or plastic.  Metal isn't necessarily a good thing, as many of the metal ones are made of the cheapest pot metal they can scrounge up.
  Brass or stainless steel would be excellent materials to use here, but I've never seen one of these things made from either metal.  The more expensive metal nozzles are heavy and usually have a powder coating which looks like paint but is far more durable.  Still, being heavy and powder coated doesn't necessarily mean it'll last a long time or that you'll be particularly happy with it.

A note about plastic:  As a general rule, plastic doesn't like sunlight.  Leave anything made of plastic out in the sun for a few months or years and it'll dry out and crack.  Hence, if you buy a pistol grip nozzle (or anything else) made of plastic, I suggest you store it indoors or otherwise out of the sunlight when not in use.

Many of the metal nozzles come with plastic or rubber wrappings around them.  This is not the same as the nozzle itself being made of plastic; if you look close at one of these "clad" models, you'll see the metal underneath where the hose connects or where the water sprays out.  The purpose of the plastic casing, other than perhaps to help protect the nozzle from getting dinged up, is to insulate it.  That means that when you're watering your flowers, your hands don't get cold holding onto that metal nozzle with cold water flowing through it.  The rubber coatings are to provide a non-slip grip, but they nevertheless also provide a bit of insulation so your hands don't get chilly.

Perhaps the most important feature of either of these claddings, though, becomes apparent when you're washing your car.  When you set a garden hose down, they have a nasty habit of getting back up all by themselves.  Nothing is more disheartening than watching that garden hose, with the metal nozzle at the end, rear up and come down smack on your paint job and take a nasty gouge out of it.  The plastic coating will help, and the rubber coating will help even more -- but only if these coatings wrap all the way around the corners of the nozzle.  One of the pistol grip nozzles sold by Ace Hardware actually comes with a separate rubber collar that you can cram onto the nose of your nozzle.  It's supposed to protect the nozzle -- there are threads on the end for connecting up another garden hose or another nozzle -- but really, who cares if the nozzle gets dinged up?  That little rubber collar is worth the price of the nozzle just for peace of mind when using it around your car!

The plunger, the shaft that goes right through the center of the nozzle and has an adjustment nut on the back end, is normally made of brass -- but there are plastic ones out there now.  Rather than be honest about selling you a cheap POS, they sometimes make the plungers out of brass-colored plastic in hopes that you won't notice.  I really don't know if the plastic ones hold up or not -- frankly, I wouldn't buy one to find out, so I'll probably never know.

The way you disassemble one of these nozzles is to unscrew a plug in the nose.  That plug, which has the hole in the center where the water comes out, is always made of plastic.  It'd be nice if someone offered one made of brass or stainless steel, but I've never seen one.  Still, plastic seems to work OK here, that part doesn't usually fail.

If you want to take your nozzle apart, you'll need to find a hex nut that fits down into the hex recess in the plug in the front, then turn the nut with a wrench. 
The items that keep the nozzle from leaking are an O-ring at the back end and a flat rubber washer at the front end.  If your nozzle leaks, replace whichever or both.  The O-ring is easy to find, any auto parts store can help you.  The flat rubber washer might be a little tougher to find, but sometimes you can fix it by simply flipping it over.  While you have the nozzle apart, I'd also suggest applying a bit of plumber's grease -- available at any hardware store -- to the surface of the part of the plunger that slides through the O-ring.  It'll make the nozzle work more smoothly and help the O-ring last longer.

If you're throwing a nozzle away, you might as well take it apart.  The brass plunger is usually in good shape, and it might fit in the next nozzle you need to fix!