BowFlex 840 vs Bells of Steel adjustable kettlebell: a dial you turn against a bell you can swing

The decision is how often you change the weight

Everything else about these two bells follows from one question that has nothing to do with specs: inside a single training session, how many times do you want a different weight in your hand?

If the answer is four or five times — a press ladder, a complex that drops weight as the reps climb, two people of different strength sharing one bell — then the mechanism matters more than the bell does. The BowFlex changes by turning a dial on the base while the bell sits on the floor. It takes about as long as re-tying a shoe, and it is the only reason to accept a plastic shell.

If the answer is once, or once a month, then the mechanism is nearly irrelevant and the shell is the whole purchase. The Bells of Steel bell changes weight by opening a screw with the supplied Allen key and swapping iron plates inside a steel competition-shape shell. Call it under a minute. In exchange you get a 35 mm handle and the same external shape at every setting, which is what makes cleans, snatches and get-ups feel identical whether the bell reads 12 kg or 20.5 kg.

That is the whole comparison in two sentences. The rest of this page is what each trade-off actually costs you.

Side by side

What the plastic shell actually costs you

Not durability in normal use. A dial-adjust bell set down under control on a mat, session after session, is fine, and the BowFlex has been on the market long enough to be a known quantity rather than a gamble.

What it costs you is the two things a kettlebell is uniquely good at. The first is drop tolerance. A cast iron bell can be set down hard, dropped on a rubber mat at the end of a brutal swing set, and knocked against a concrete slab without anyone caring. A plastic shell over a weight stack cannot, and that changes how you finish a set — you have to put it down nicely at the exact moment you least want to.

The second is shape. A kettlebell is a handle over a ball of offset mass, and the offset is the point: it is what makes the swing a hinge and the clean a rotation rather than a curl. A dial-adjust bell is a box with a handle, and it is a wide, flat handle at that. For swings, goblet squats, rows, presses and carries — most of what most people do — this is a non-issue. For snatches and high-rep single-arm cleans, where the bell has to rotate cleanly around the back of your wrist, it is a real difference, and it is why our adjustable vs standard page argues for fixed bells whenever space allows.

What the steel shell actually buys you

Three things, in order of how much they matter.

A constant handle and a constant shape. At 12 kg and at 20.5 kg the handle is 35 mm and the shell is the same size. Nothing about the lift changes as you get stronger — the rack position, the clean path and the insertion on a snatch are identical. On cast iron, the shell grows and the handle thickens with the weight, so every jump is a slightly new skill. That is the same argument our cast iron vs competition page makes, except here you get it without buying five bells.

Half-kilo micro-loading. This sounds like a specification and is actually a training feature. Overhead pressing is the lift where kettlebell progress stalls, because the standard jump between fixed bells is 4 kg — about 9 lb — which is an enormous increment on a one-arm press. Half-kilo steps turn a wall into a ramp.

A ceiling you can raise. Two-handed swings and goblet squats outgrow 40 lb quickly. If you train seriously for a couple of years, a bell that stops at 40 lb becomes a warm-up bell and you buy a heavy bell anyway. As sold, the Bells of Steel bell runs to 45.2 lb — past the BowFlex, though not by much — and a separate expansion kit adds 13 kg of plates to the same shell for a 70.5 lb ceiling. The BowFlex has no such path: 40 lb is where it ends.

The cost is money and a wrench. It is the most expensive adjustable on this site, it starts at 12 kg so it is useless as a beginner's light bell, and changing weight is a deliberate act rather than a reflex.

Which one fits a small space better

Both of them, which is the entire point of an adjustable — but differently.

The BowFlex wins on pure footprint and on how it lives in a room. At 8.8 x 7 x 12.5 in. it goes under a desk or in a closet, it does not look like gym equipment, and it never rings when you set it down. For a studio apartment where the training space is also the living space, that is worth real money.

The Bells of Steel bell is 8.25 in. wide and 11 in. tall, so it is barely larger — but loaded it is 45.2 lb of steel and iron, which is a different object to move and a different thing to set down on a floor you do not own. If you are upstairs from somebody, the honest answer is a mat under the working area and a rule that the bell never leaves your hand above knee height. Kettlebells in an apartment covers the floor and noise question properly.

Neither bell needs a rack, and that is the real small-space win. Three fixed bells covering the same range need somewhere to live, and a corner with three bells in it is a corner you stop walking through.

The case for buying neither

Adjustable kettlebells solve a storage and money problem, and they create a training one: you can only ever hold one bell. Double kettlebell work — double front squats, double cleans, double presses, the farmer carry — needs two bells of the same weight, and no adjustable gives you that at any price.

So if you already own a 16 kg or 20 kg bell and you are thinking about an adjustable to fill in the rest, stop and price a second fixed bell first. A matched pair in your working weight opens a whole category of training that one adjustable cannot touch, and it usually costs less than either bell on this page. The main kettlebell roundup is where to go for that, and the sizing page works out what weight the second one should be.

The other case for neither is simpler: you do not know what weight you need yet. That is an extremely common and entirely reasonable position, and the right response is not to spend serious money on range. It is to buy the cheapest cast iron adjustable that covers the beginner window, train for three months, then buy the bell you have learned you want.

Where the Yes4All adjustable fits

It is on this page because for a lot of readers it is the correct answer to a comparison between two bells they should not buy yet. It is cast iron rather than plastic, powder-coated with no welds, it covers 10 to 40 lb in six settings, and it costs a fraction of either bell above.

What it gives up is everything the other two are being paid for: the plate change is manual and slower than the BowFlex dial, the handle is wider than a competition bell so it is not the one to snatch with, and the 40 lb ceiling is the same one the BowFlex has. It is a good first adjustable and a bad last one. Our adjustable kettlebell roundup ranks all three against the full rubric if you want the scoring rather than the verdict.

The verdict

For most people reading this site — a corner of a rented apartment, one bell, a few sessions a week — the BowFlex 840 is the better buy of the two. The 8 to 40 lb range covers the window where most training actually happens, the footprint is the smallest, and the dial genuinely changes how a session flows when you are working a press ladder alone.

The Bells of Steel bell is the better bell, and it is the right purchase for a narrower buyer: somebody who already knows they hinge, press and clean regularly, who wants competition geometry, and who would otherwise buy four bells over the next two years. Over that horizon the price stops looking unreasonable — but only over that horizon.

And if budget is the live constraint, buy the Yes4All, spend the difference on a mat, and come back to this page in a year when you know what you need.