There are many variables to consider when choosing a bar. Here are some questions that you might be asking:
Do you choose a 25 mm, 28 mm bar, 28.5 mm or 29 mm bar or do you go even thicker?
What is bar whip and do you need it?
What finish is best for you?
What knurling texture will best suit you?
Olympic Competition bars are 25 mm in diameter for women and 28 mm for men. These diameters have 2 effects. First they allow most people to properly perform a hook grip. Second, the thinner steel is able to “whip”. A hook grip, where your thumb is gripped between the fingers and the bar, is not only stronger, it allows you to grip the bar while keeping your forearms somewhat relaxed. When your arms are relaxed you are much more able to perform the rapid movements required for the clean and the snatch. The whip in the bar allows an advanced lifter to use the bar as a spring by taking advantage of the fact that the bar bends under the load and acceleration and then springs back to it’s original shape.
It takes stronger steel to reach the same strength as a 28.5 mm or higher diameter with a 28 mm bar and therefore these bars are typically more expensive if made to stand up to the demands of Olympic lifting.
28.5 mm bars still allow athletes to use a hook grip and whip pretty well, but not as well as 28 mm bars. 28.5 mm also works well for Powerlifting. Therefore many hybrid, general purpose or CrossFit bars have 28.5 mm shafts. Most of the bars used for men at the CrossFit Games for the past several years have been 28.5 mm.
Most dedicated Powerlifting bars are 29 mm. They do not make separate bars for men and women, since a hook grip is not required. Athletes use an alternating grip for deadlift that allows nearly any hand size to grip effectively.
29 mm bars are much stiffer than 28 mm bars so some of the whip of an Olympic competition bar is lost in a Powerlifitng bar. In competion the whip is not needed as much since the power lifts are not as dynamic as Olympic lifts, although some people do use the whip to get out of the bottom of a squat.
The thicker a bar gets, the more comfortable it feels on your shoulders for back squats and the easier it is for a bar manufacturer to make a really strong bar. Also gripping a thicker bar will help develop grip strength. Rogue sells bars with diameters as high as 50 mm specifically to work on grip strength.
An uncoated bar often offers the best grip available without having to make a sharp knurl that will tear up your hands. However, if you live in a humid climate or near the ocean, the bar will quickly rust unless it is made out of stainless steel which is much more expensive. The rust will not affect the performance of the bar unless it is excessive, but it will discolor the bar which is a problem for many people.
Chrome offers rust resistance, but is generally more slippery than uncoated steel. However, there are many types of chrome and if done well the grip can be quite good. Many of the best bars in the world have a chrome finish.
Nearly everyone agrees that the best knurling texture for Olympic lifting is a fine knurl that is not sharp. This is accomplished by closer spacing of the cuts and deeper cuts than you will see on the bar that comes with the 300 pound weight set from your local sporting goods store. Knurling like this takes precision equipment and is time consuming to create, which is one of the things that makes bars like this so special.
There is less consensus in the Powerlifting world with respect to knurling texture. Some athletes like the same knurling texture as the Olympic lifters. However, some prefer a slightly sharper knurl that comes from making the cuts a little deeper. Rogue sells power bars with both styles of knurling.
The Olympic style knurling seems to be perfect for CrossFit movements and workouts which is why most quality bars aimed at the CrossFit market have this texture.
Once you know the answers to these questions, you can find the perfect bar to suit your needs here.