Some strength companies are reselling shaft collars under the name Allen collars and marking them up three or four times the cost. The shaft collar (Figure A) is a steel ring collar with shallow splits in the radius. A collar of proper size can be tightly secured against any shaft simply by tightening the collar screw with an Allen wrench.
Shaft collars are available in a variety of bore (center hole) sizes: 3/4-inch, 1-inch, 11⁄2-inch, diameters, etc. The primary application of a shaft collar is to center and hold a pulley sheave onto a center rod in an industrial setting (Figure B). However, they are also serve perfectly for barbell and dumbbell collars (Figure C) and for many other applications involving strength-training equipment.
I purchased a lot of 10 shaft collars for $1.75 each from Fastenal. They are also available from Global Industrial, M.S.C. Supply, McMaster-Carr, etc. Shop around and I'm sure you'll beat the price of $29.95 for four pieces one reseller I know SHAFTS people for! Don't get shafted! LOL.
Notes from from the editor:
Since this article was written by Sticks (2014), the cost of steel and shaft collars have increased. You can still find good prices, though. For example, I found (January, 2021) that Amazon sells a package of four carbon steel, black oxide coated, single-split, 1" bore shaft collars for $13.99 + shipping (shipping is free for orders over $25).
Keep in mind that a shaft collar must have a slightly smaller bore size than the actual diameter of the shaft it is to be tightened on. For example, a 1-inch (bore size) shaft collar will work perfectly with a schedule 40 3/4-inch nominal pipe (actual outer diameter is 1.050 inches). However, if your barbell has an OD 1 inch or slightly less (as mine is), it will require a set of 3/4" (bore) collars.
Bonus: Budget Weight Holders
Need extra weight holders for your 2"x2" square tubing power rack? I saw a popular brand for sale on the net for $50.00 per pair! Figure D illustrates a much more economical set-up. It consists of two 5-inch long, one-inch diameter hex-steel bolts ($5.50 each), two bolt nuts ($0.50 each), and two one-inch (bore) shaft collars ($1.75 each). Total investment for a pair of great weight holders: $12.75 and no shipping. Sweet.