Shoulder Boulder/Chest Fly Attachment

Name: Shoulder Boulder/Chest Fly Attachment
Brand: Bells of Steel
Rating: 4.33 (5 reviews)

Bells of Steel’s Shoulder Boulder is a rack-mounted, plate-loaded arm for lateral raises, front raises, rear delt flies, and chest flies — a cam-style alternative to dumbbells that keeps tension on the delts through the whole range instead of dropping off at the top and bottom.

A 360° pop-pin dial sets the arm’s starting angle, so you dial in where resistance kicks in per exercise; the pivot rides on bronze bushings and a sealed ball bearing for a smooth pull. It mounts to a single upright on any 3x3” rack with 5/8” or 1” holes (Bells also sells a 2.3” version for cable towers and all-in-one trainers), so it adds no floor footprint — the tradeoff independent reviewers note is that the loaded arm is a bit tedious to reposition between uprights and can’t do inward-rotation moves like pullovers.

For a similar cam-based rack attachment, see the Dragonfly Rack Mounted Multi Flight Attachment or the budget Mikolo 2-in-1 Lateral Raise & Chest Fly Attachment.

Use	lateral raise, front raise, rear delt fly, and chest fly rack attachment
Mount	3x3 in racks, 5/8 in or 1 in holes (60mm/2.3 in version for cable towers and all-in-ones)
Weight	36 lbs (attachment only)
Capacity	165 lbs per side
Material	14-gauge powder-coated steel; bronze bushings + sealed ball bearing on the pivot
Resistance	plate-loaded, cam-adjustable via 360 deg pop-pin dial

What is a Rack Attachment?

What rack attachments are

Rack attachments bolt or pin onto a power rack or squat stand to expand what it can do — J-cups and safety arms/straps (the essentials), plus dip bars, a landmine, a lat pulldown, weight-plate storage, roller J-cups, and more. They turn a rack into a whole gym.

Compatibility comes first

An attachment must match your rack’s upright size (2x2, 2x3, or 3x3) and hole pattern/hardware (e.g. 5/8-in vs 1-in holes, Westside spacing). Attachments are usually series-specific — a Monster Lite J-cup won’t fit an Echo upright — so confirm the fit before buying.

How it compares

	Shoulder Boulder/Chest Fly Attachment	Monster Matador	Fat Grip Parallel Landmine Handle	Stealth Spotters
GymRadar rating	4.33/5	4.33/5	4.33/5	4.33/5
Price	$322.99	$195.00	$64.97	$550.00
Use	lateral raise, front raise, rear delt fly, and chest fly rack attachment
Mount	3x3 in racks, 5/8 in or 1 in holes (60mm/2.3 in version for cable towers and all-in-ones)
Weight	36 lbs (attachment only)		13.5 lb
Capacity	165 lbs per side
Material	14-gauge powder-coated steel; bronze bushings + sealed ball bearing on the pivot		0.25" steel, seamless tube construction	hand-welded American steel; 3/8" mounting channel, 1/4" laser-cut vertical face
Resistance	plate-loaded, cam-adjustable via 360 deg pop-pin dial

4.3/5 · 5 GymRadar reviews

Reviews by source

Expert	4.33/5	5 reviews
Retailer	4.8/5	31 reviews
Youtube	4.3/5	2 reviews

The Shoulder Boulder is a solid, honestly-priced take on the rack-mounted delt/chest-fly cam attachment — its functionality stands out, giving dumbbells’ natural range a real resistance curve you can dial in per exercise (pop-pin start angle) instead of losing tension at the top or bottom. Build quality is its weakest dimension: reviewers call the powder coat and welds “budget-level” next to Rogue or REP, though the bronze-bushing/ball-bearing pivot itself feels smooth. It’s a clear value pick against thousands-of-dollars standalone machines, with the main tradeoffs being a loaded arm that’s tedious to reposition between uprights and no inward-rotation movements like pullovers.

+Functionality: cam-adjustable pop-pin dial sets the resistance curve's start angle per exercise, unlike a dumbbell's fixed gravity curve (Jungle Gym Reviews, Bells Shoulder Boulder review)
+Functionality: smooth pivot on bronze bushings and a sealed ball bearing (Bells Shoulder Boulder review)
+Versatility: works lateral raises, front raises, rear delt flies, and chest flies from one compact attachment (Jungle Gym Reviews, manufacturer)
+Value: about $300 vs. thousands for a standalone multi-flight machine like Temple of Gains (Bells Shoulder Boulder review, Jungle Gym Reviews)
+Versatility: mounts to any 3x3 in upright with 5/8 in or 1 in holes, adding zero floor footprint (manufacturer, Jungle Gym Reviews)

−Build quality: powder coat and welds are "budget-level" next to Rogue or REP (Bells Shoulder Boulder review)
−Functionality: no inward-rotation movements (pullovers, pec squeeze) due to a fixed stopper (Bells Shoulder Boulder review)
−Versatility: loaded arm is tedious to reposition between uprights — video reviewer notes his wife can't lift it loaded (Bells Shoulder Boulder review)
−Functionality: chest-fly resistance curve feels less even than lateral raise, since range of motion extends past where gravity gives good tension (Jungle Gym Reviews)
−Durability: little independent long-term-use data yet — coverage is limited to launch-window reviews

$322.99

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