Much of how a lifter classifies knurling seems to depend on what bars he/she has used and his/her barbell sport background. Perhaps someone who has a powerlifting background and lifted with a specialized powerlifting bar for years can have a different opinion of what aggressive knurling is. The best knurl grade for you will be what you are accustomed to in most instances.
A point of marketing that has surfaced recently is the notion that clean, defined borders of knurling is somewhat indicative of higher quality. The reality of these prominent lines is that this effect can be created in such a way that compromises the steel strength of the barbell.
Knurling is cut into the barbell with a CNC Lathe. Some lathes will require more manual handling than others. The borders of the knurling are created where the machine stops and is restarted again. A fully robotic machine can make exact adjustments during this process, whereas a barbell that is hand-crafted by a man must be reset manually. What some barbell manufacturers will do, (even with some IWF certified bars), is they’ll cut the lines after the knurling is done to create a nice, super neat border. This looks great, and internet bloggers will certainly say this “high quality” feature is a positive attribute of the barbell. The main issue is that any physical cut in to steel is an opportunity to weaken it because it creates stress points. Multiple, unnecessary stress points along the barbell shaft are detrimental to steel strength and the higher the tensile strength of the material, the greater the problem this creates.
Many lifters will like the traditional centre knurling featured on many barbells. Some consider the extra grip they feel on the back of their t-shirt ideal because it makes the bar feel more secure when squatting. The actual purpose of the centre knurling on barbells dates back to when one-armed “odd” lifts were part of competitive weightlifting and even included in the inaugural Olympic games in the late 1800's. The one-armed snatch and the one-armed clean and jerk are only a few examples of lifts that required such knurling. You’ll notice that 15 kg barbells don’t feature a centre knurling because women were not included in weightlifting competitions until well after the one-armed lifts were phased out. For most Olympic weightlifters, the centre knurling will be an annoyance so many higher end weightlifting bars will have a recessed centre knurling for this reason. The IWF specifies the centre knurling is still a requirement for 20 kg barbells, so manufacturers produce their bars to meet this requirement.
Barbell Finishes and Their Properties
Here is a list of many barbell finishes and their pros and cons:
Black Zinc: Looks Great. Wears (down) easily. Often times it is difficult to make black zinc appear to be truly black. Typically you will end up with a somewhat charcoal to chocolate finish or somewhat of a dark olive colour.
Black Oxide: Has a matte black appearance. Black oxide is not so much a coating as it is a chemical process of turning steel black. It has very little anti-corrosive properties which means it will rust quickly if not cared for properly. It will scratch, but it does not flake off. The scratches are just a lighter or a different shade of black so they show more. Black oxide does leave the barbell with a raw steel feel without being purely raw steel.
Bright Zinc: Looks great and classic. It can vary from very shiny, almost chrome-like in appearance to a more matte finish. Exhibits a higher resistance to corrosion than black zinc. Bright Zinc will tarnish and turn grey over time. It is considered a sacrificial coating as it oxides itself rather than the steel underneath it. It will eventually develop a patina which makes each bar have its own unique look depending on its use.
Nickel Chrome: Looks great and classic. Chrome will scratch or chip if mistreated, but it typically lasts a lifetime. All higher end weightlifting bars are nickel chrome or hard chrome plated.
Hard Chrome: Hard chrome is actually an industrial finish. Although it can be polished to high lustre , it will not have the aesthetics of nickel chrome. Hard Chrome has a couple of advantages over Nickel Chrome. It does actually fortify the bar and increases the overall tensile strength. It will easily last 20 years or more. The disadvantage of Hard Chrome is that it can have slight marks in it where the components are suspended by a thin wire during the electroplating. Due to Hard Chrome being so thick, even a small imperfection can be made more noticeable where the material accumulates.
Thin Dense Chrome: It has a matte dark grey appearance that is very unique looking. It has the feel of raw steel without the rust problems of bare steel or some of the other coatings. It adds tensile strength to the barbell just like Hard Chrome does.
Bare/Raw Steel. It looks really great and feels great... for about a week, then it will start to oxidize and rust. If you don't like oiling barbells and meticulously caring for them, or don't mind lifting a rusty bar, a raw piece of steel is ideal for you. With routine oiling, wiping perspiration from the bar after each use, and storing it in a climate controlled environment, the steel will develop a nice bronze/grey coloured patina.
Barbell Rotation Types
Bronze Bushings, Composite Bushings, Needle Bearings
Composite Bushings are made from hard plastic compounds. They are actually harder than bronze and will not break down after extensive use. Over time, the spin of the bar won’t improve (like with the Oilite Bushing), it will remain consistent
Needle bearings provide the smoothest and quickest bar rotation. There are a number of barbell varieties with either 10 or 8 needle bearings being the most common variety. We have found the quality, grade, and fit of the bearings as well of type of lubricant used has more impact on spin than total number of bearings.
Eight (8) bearings can actually take up as much space as Ten (10) bearings, depending on size of the bearings. Bearings are available in different load ratings and widths. Higher load bearings may not spin as easily unloaded and lighter load bearings usually spin much quicker without load, such as spinning with the hand. Once the bar is loaded, there will be no discernible difference in speed of rotation. The higher load rating bearings will last longer and can absorb more impact shock. The reality of weightlifting is that the bar only turns over 180 degrees during a proper lift, and although weightlifting is fast, it's relatively slow as far as revolutions per minute (rpm). Needle bearings are really designed for super high speed applications, meaning thousands of rpm's per minute. Although weightlifting doesn’t push needle bearings to the full capacity of what they are designed to do, utilizing these bearings can still contribute to a successful lift.