Pros:Easy to use, reliable, no slop or play, built to last a lifetime.
Cons:Knockoffs are available for half the price.
The Bottom Line: Irwin's Vise-Grip brand locking chain clamp is great for holding and torquing round or irregular objects. It costs more than other brands, but is extremely well-built and warranteed for life.
There are some tools that you don't need for most jobs, but when you do need them, nothing else will do. A good chain clamp, sometimes called a "chain whip", is one such tool. I didn't consider it a toolbox necessity, especially with a strap wrench to hold pulleys and other round objects, but I found myself walking to the nearest hardware store to buy one while "stuck" changing the timing belt in my Hyundai. After having removed the crank pulley, I set it aside and put the retaining bolt back into place, leaving only the sprocket. The bolt tightened (of course) while turning the engine by hand.
Recommend this product?
A strap wrench is great for gently holding round objects. Gentle is relative; I'm fairly certain one could use a strap wrench to tear someone's arm off or, to pick a less gruesome example, twist a branch from a tree. But it's difficult to hold round, hard objects tightly, and straps stretch to the point where breaking out a tightened bolt merely tugs the strap. The smaller the object, the worse this problem is, due to the inherent bulk of a strap wrench. (A smaller strap wrench would help, but small strap wrenches tend to be made of plastic.) I could barely get a good grip on my crank pulley using a strap wrench, and even then the strap had too much give to remove the bolt.
But with Irwin Tools's Vise-Grip brand chain clamp, getting the crank bolt out was easy. It's less bulky than a strap wrench, and 500 pounds of clamping force provides more than enough friction to hold smooth metal tight. That the chain is less smooth itself than a strap helped to grip the sprocket as well, but a sprocket isn't a typical surface. Most importantly, the chain has far less give than a strap; torquing the object being held doesn't cause the chain to stretch.
I paid roughly $40 at an Ace Hardware for the Vise-Grip chain clamp. Knockoffs are available at Harbor Freight and many other stores for less money, but, just like off-brand locking pliers, these tend to have more play, and also to not come with the Vise-Grip lifetime guarantee of replacement if the tool fails due to defects during normal use. Nor are replacement chains, springs, and adjusting screws as readily available for the knockoffs.
The chain on the Vise-Grip locking chain clamp runs smoothly and with very little side-to-side motion. Similarly, the clamp body, essentially a modified Vise-Grip locking pliers, adjusts, locks down, and releases smoothly, with no play at all. This is a solid-feeling tool, and by "solid" I don't mean "heavy". A 5 mm hex socket in the adjusting screw allows for fine adjustment while in use. Although advertised as "9 inch", the maximum diameter round object that can be gripped by this tool is 6 inches, as it has a 19" chain. (The size of irregular objects that can be gripped may vary; figure that the perimiter should be an inch or two less than 18".) An extension chain, doubling the diameter, is available separately.
In addition to its obvious under-hood applications, a chain clamp can also be used as an impromptu pipe wrench or, gently, for most strap-wrench tasks, including removal of oil filters spun on too tightly to remove by hand. I'm fairly certain it could open the pentagonal valve atop a fire hydrant or remove the bolts at the bottom of a lamp post, but I don't recommend that kind of mischief. What it can't do is remove or install bicycle sprockets onto threaded cartridges or hubs. A specialized chain whip made from bicycle-gauge chain is needed instead for this task. As the clamping force on both the Irwin Vise-Grip chain clamp and the off-brand equivalents is delivered to the chain pin, there's no straightforward way to adapt the tool to bicycle chain without ruining it for other applications.
If you do a lot of auto or machine maintenance and repair yourself, it'd be good to have a chain clamp in your toolbox, so as not to have to make a run to the store to buy one with the job half-done. And if you have the Irwin Vise-Grip chain clamp, chances are low that you'd have to make a tool-shop run because your tool broke mid-job.