BON4M Stainless Steel Cage
The BON4M scores 8.5/10 in our testing — best-in-class security (10/10) from solid 304 stainless steel construction. Weighs 233g with 21 fit configurations (7 rings + 3 spacers). Not for beginners; best for experienced users seeking a permanent, escape-proof device at $219.
Check Price →BON4M Stainless Steel Cage Review: The Heavyweight Champion of Security?
A data-driven analysis of durability, comfort, and why this 233g beast is not for everyone.
Reviewed by LockedCage Team · Feb 13, 2026 · 8 min read · Based on 30-day testing
Available at bon4.com · Free shipping on orders over $79
LockedCage Score
8.5 / 10
Virtually escape-proof
Heavy, needs acclimatization
Open design, easy clean
Premium price, premium build
7 rings, 3 gap spacers
Verdict: Best for Experienced Users
Top-tier security and build quality. Not recommended for beginners due to weight and fitting complexity.
Is the BON4M Right For You?
The BON4M isn't a toy. It's a premium, medical-grade stainless steel device designed for absolute denial. While popular alternatives like the HolyTrainer focus on lightweight comfort, the BON4M prioritizes weight and security. At 233g, you'll feel every gram — and that's exactly the point. If $219 is above your budget, the CB-6000S at $75 lets you learn your sizing first, though expect quality compromises in material and security.
The Good
- Indestructible: Solid stainless steel. Can't be cut, broken, or forced open.
- Hygienic: Open-bar design allows cleaning without removal. No odor buildup.
- Secure: Hinged ring design prevents escape. Padlock included.
- 21 fit combos: 7 ring sizes + 3 gap spacers = dialed-in customization.
- Built to last: No degradation, no yellowing, no material fatigue — ever.
The Bad
- Heavy (233g): You will feel it swinging. Running requires a support strap.
- Cold in winter: Metal conducts temperature. First contact in the morning is bracing.
- Premium price: At ~$219, it's 4x the cost of a resin starter cage.
- Not beginner-friendly: Requires precise measurement. No forgiveness for wrong sizing.
- Hair pinching: The base ring can trap body hair. Grooming recommended.
Ready to explore premium stainless steel?
Check Price on BON4.comCritical Sizing Warning: Don't Buy Blindly
Metal cages are unforgiving.
Unlike resin, steel does not flex. If you buy the wrong ring size, it will hurt. Circulation issues, skin pinching, and inability to remove the device are real risks with incorrect sizing.
The BON4M ships with 7 hinged back rings (40mm to 52mm inner diameter) and 3 gap spacers. That's 21 possible configurations — but you still need to know your baseline measurements to pick the right starting point.
Free Tool
Unsure if the 40mm or 45mm ring is right?
Our AI Cage Check analyzes the BON4M's exact dimensions against your body measurements and predicts fit, comfort, and security scores.
Launch BON4M Fit Calculator| Model | Flaccid Length | Internal Cage Length |
|---|---|---|
| BON4Micro | 1.4" – 2.6" (35–66mm) | 1.4" (35mm) |
| BON4M | 2.6" – 4.0" (66–102mm) | 2.56" (65mm) |
| BON4ML | 4.0" – 5.2" (102–132mm) | 3.15" (80mm) |
| BON4MXL | 5.2" – 6.6" (132–168mm) | 4.53" (115mm) |
| Spec | BON4M |
|---|---|
| Material | Medical-grade stainless steel |
| Assembled Length | 3.65″ (93mm) |
| Internal Cage Length | 2.56″ (65mm) |
| Cage Opening Diameter | 1.42″ (36mm) |
| Weight (assembled) | 8.22 oz / 233g |
| Ring Sizes | 7 hinged rings: 40, 42, 44, 46, 48, 50, 52mm |
| Gap Options | 3 spacers: 0.33″, 0.43″, 0.53″ |
| Lock Type | Stainless steel padlock (2 keys) |
| Shipping | Discreet FedEx from Netherlands. Free over $79. |
Real-World Performance
The “Weight” Factor
At 233g, the BON4M is significantly heavier than a CB-6000S (~100g) orHolyTrainer V4 (~80g). For some wearers, this constant “gravity tug” is a feature, not a bug — a persistent, pleasurable reminder of denial. For runners and gym-goers, it requires a support strap or jockstrap to prevent bouncing.
Long-Term Wear & Sleep
Can you sleep in it? Yes, but give it about 2 weeks to acclimatize. The hinged ring is a genuine game-changer here — it prevents the “skin pinching” at night that plagues cheaper solid-ring metal cages. Nocturnal erections will wake you during the first week; this fades as your body adjusts.
Wear loose-fitting boxer briefs or sleep shorts. The testicles hang more naturally in warm, loose clothing, which reduces pressure on the base ring overnight.
Hygiene & Maintenance
This is where metal demolishes resin. The BON4M's open-bar design means you can shower, soap, and rinse without removal. No trapped moisture, no bacterial colonies forming in hard-to-reach corners. After 30 days of continuous testing, there was zero odor — something we can't say about any resin cage we've tested past the 2-week mark.
Security Assessment
We scored the BON4M 10/10 on security. The combination of medical-grade steel construction, hinged locking ring, and included stainless steel padlock makes this effectively escape-proof without tools. The cage bars are too narrow for pullout, and the hinge mechanism eliminates the “twist and slide” exploit that defeats many cheaper cages.
BON4M vs. The Competition
vs. HolyTrainer V5 (Resin)
ComparisonOur take: If you want sleep comfort: choose HolyTrainer. If you want total security: choose BON4M.
BON4M wins on:
Security, durability, hygiene, no odor
HolyTrainer V5 wins on:
Weight (80g vs 233g), comfort, price ($50 vs $219), discretion
vs. CB-6000 (Polycarbonate)
ComparisonOur take: BON4M is cleaner, stronger, and won't develop odor after a month. CB-6000 is cheaper but feels cheaper.
BON4M wins on:
Build quality, hygiene, no pinching (hinged vs H-ring), longevity
CB-6000 wins on:
Price ($100 vs $219), lighter weight, widely available
vs. Cheap Amazon Steel Cages ($20-40)
ComparisonOur take: Don't risk it. BON4M's finish is mirror-smooth. Cheap cages have sharp edges, rough welds, and poor ring tolerances that can cut skin.
BON4M wins on:
Finish quality, safety, ring options, customer support
Cheap Amazon Steel Cages wins on:
Price only
See how the BON4M compares in our full database.
Find the Best Deal on BON4MWhat Verified Users Say
“Perfect for permanent wear, comfortable, and heavy duty. Might not be for you if you're whiny or new to this.”
“After extensive testing, I can say that the Bon4M is a top tier chastity cage. If you choose the correct size for the wearer, it's unbeatable.”
“Great quality product, very enthusiastic about the two cages I've bought. As a long term wearer of other cages, I recognise the quality of these.”
“It's a little too heavy sometimes, so you have to hold it up with a strap or something. It sticks out a lot farther under clothes than other cages.”
“I've tried a lot of the usual cages (legit holy trainer, vice, bon4m)... long term wear this one has been the best in my experience.”
References
- [1]ASTM F138-19a: Standard specification for wrought 18Cr-14Ni-2.5Mo stainless steel bar and wire for surgical implants — the benchmark for medical-grade steel used in the BON4M — ASTM International
- [2]ISO 10993-10:2021: Biological evaluation of medical devices — Tests for skin sensitization and irritation from prolonged metal contact — International Organization for Standardization
- [3]NICNAS safety assessment of nickel release from consumer products in prolonged skin contact applications — Australian Government NICNAS
- [4]EU REACH Regulation Annex XVII Entry 27: Nickel release limits for articles intended for prolonged skin contact (max 0.5 ug/cm2/week) — European Chemicals Agency (ECHA)
Common Questions
The BON4M is a heavy stainless steel device (233g) that requires precise fitting. We recommend lighter resin cages for first-timers. If you're set on metal, start with shorter wear sessions and use our AI Sizing Tool to verify your measurements before buying.
The BON4M ships with 7 hinged ring sizes (40-52mm) and 3 adjustable gap spacers, giving you 21 possible configurations. If none work, BON4 offers sizing guidance directly. We recommend using our Cage Check tool to simulate fit before purchasing.
The hinged ring design significantly reduces pinching compared to solid-ring cages like the CB-6000. However, users with significant body hair may experience irritation around the base ring. Lubricant and regular grooming help.
Daily: shower normally and use liquid soap with a soft toothbrush. Weekly deep clean: disassemble, soak in 70% alcohol, then boil for 2-3 minutes. Stainless steel is inherently antibacterial and won't develop the odor problems common with resin cages.
Yes. The BON4M is specifically designed for extended wear. The open-cage design allows hygiene access, and the stainless steel won't degrade over time. Most users report full acclimatization within 2 weeks.
No. The BON4M uses medical-grade stainless steel that is highly resistant to rust, tarnish, and discoloration. With basic maintenance (rinse and dry after showering), it will look new for years.
No. The BON4M will trigger metal detectors and body scanners, resulting in a secondary screening and pat-down. TSA officers may ask you to explain the device. For air travel, switch to a non-metallic cage (resin or silicone) before your trip.
See Also
Related Reviews
Ready for the ultimate steel experience?
The BON4M is built for wearers who demand maximum security and are willing to invest in quality. Free discreet shipping on orders over $79.