Bells of Steel builds its Hydra and Manticore racks from true 3×3″ (76.2 mm) 11-gauge tube, the same nominal size as Rogue and REP’s 3×3″ racks. Hydra uses 5/8″ holes, like Rogue Monster Lite and REP PR-4000. Manticore uses 1″ holes, like Rogue Monster 2.0 and REP PR-5000, and adds 5/8″ side keyholes that take Hydra attachments. So single-hole attachments usually cross over when the hole size matches. The things that block a swap are attachments with a second locking pin, Hydra’s 6″ side-hole spacing, and Bells of Steel’s separate 2.3″ racks, which almost nothing else fits.
Every spec below comes from Bells of Steel’s, Rogue’s, REP’s, Titan’s and the attachment makers’ own pages, checked October 17, 2026.
Disclosure: links marked “affiliate” go to Bulletproof Fitness Equipment or Exponent Edge, whose affiliate programs Hypertrophy Protocol is in. If you buy through them, Hypertrophy Protocol may earn a commission at no extra cost to you. Links marked “referral” go to Beyond Power, which has no affiliate program; buying through them may earn Hypertrophy Protocol referral credit.
Hydra vs Manticore vs the 2.3″ line: the specs that decide fit
| Spec | Hydra | Manticore | 2.3″ line (Residential, Light Commercial) |
|---|---|---|---|
| Upright | True 3×3″ (76.2 mm), 11-gauge | True 3×3″ (76.2 mm), 11-gauge | 2.3×2.3″ (60 mm) |
| Holes | 5/8″ | 1″, plus 5/8″ side keyholes | 5/8″ |
| Front hole spacing | 1″ in the bench and pull zone, 2″ elsewhere | 2″ throughout | Light Commercial: 1″ in the bench and pull zone, 2″ above and below. Residential: not stated |
| Side holes (72″ and taller uprights) | 2″ near the top and bottom, 6″ through the middle | 5/8″ side keyholes (“four-way holes”) | Not stated |
| Rack heights | 72″, 84″, 90″ or 108″ | 72″, 84″, 90″ or 108″ | 84.5″ or 72″ |
| Depths | Not stated in text (spec sheets are images) | 17″, 24″, 30″ or 43″ | Light Commercial: 39″ |
| Width | 47″ or 49″ | 49″ | Not stated |
| Rated capacity | 1,000 lb bolted down or otherwise secured | 1,000 lb bolted down | Residential 700 lb; Light Commercial 880 lb static (600 lb warrantied) |
Sources: Bells of Steel’s Hydra upright page, Hydra 101, Manticore 101, Residential and Light Commercial rack pages. Bells of Steel doesn’t call the Hydra’s spacing “Westside,” but its 1″ bench-zone spacing is the same idea.
What “true 3×3” means for fit
Bells of Steel’s attachment compatibility FAQ says Hydra attachments fit “true 3″ x 3″ (76.2mm x 76.2mm) tubing with 5/8” holes” and Manticore attachments fit the same tube with 1″ holes. It also says many imported “3×3” racks are actually 75 x 75 mm, because imported racks use metric steel. Bells of Steel’s attachments usually still fit those racks, but the FAQ warns they “will not be a super snug fit.”
That FAQ doesn’t name any brand as metric, and neither do the makers. REP lists the PR-4000 and PR-5000 as 3×3″ 11-gauge, Rogue lists its Monster lines as 3×3″ 11-gauge, and Titan lists the X-3 as 3×3″ 11-gauge. None of them publishes a millimeter size. A 75 mm tube is 1.2 mm narrower per face than a true 3×3″, which is easy to miss with a tape measure. Power rack upright sizes shows the difference to scale.
The FAQ doesn’t cover the reverse case. A sleeve-style attachment built closely around a 75 mm tube has less room on a true 3×3″ upright, so for anything that wraps all four sides, ask the attachment maker before you assume it slides on.
Which other racks match Hydra or Manticore
| Rack | Tube | Holes | Front spacing | Closest Bells of Steel line |
|---|---|---|---|---|
| Rogue Monster Lite | 3×3″, 11-gauge | 5/8″ | Westside: 1″ through the bench and pull area, 2″ above and below | Hydra |
| REP PR-4000 | 3×3″, 11-gauge | 5/8″ | 2″, with 1″ in the bench zone | Hydra |
| Rogue Monster 2.0 | 3×3″, 11-gauge | 1″ | 2″ on center (Rogue’s category page says Westside; its product guides say 2″) | Manticore |
| REP PR-5000 | 3×3″, 11-gauge | 1″ | 2″ throughout | Manticore |
| Titan X-3 | 3×3″, 11-gauge | 11/16″ | Westside, with 6″ side spacing | Closest to Hydra, not confirmed (Titan’s own X-3 pins are 5/8″) |
Sources: REP’s rack guide, Titan’s power rack comparison and Rogue’s Monster pages, as summarized in REP PR-4000 vs Rogue Monster Lite. The Titan X-3 is the odd one: it has 11/16″ holes, and Titan’s own X-3 mag pins are 5/8″ (16 mm), so 5/8″ Hydra parts are the closer match. Titan doesn’t say other brands’ attachments fit, so treat it as unconfirmed. Titan X-3 attachment compatibility covers that rack in detail.
Where two-pin attachments miss
Bells of Steel’s FAQ gives the split squat roller as its example: it has an extra locking pin, and “if your rack does not line up the hole pattern, then the locking pin will not work.” Matching tube and hole size handles the first pin. The second pin depends on hole spacing.
- From a 2″ rack to Hydra: usually fine on the front face. Hydra’s 1″ bench zone still has a hole at every 2″ step, and the rest of the upright is 2″.
- From Hydra to a 2″ rack: this is the direction that misses. A part designed around 1″ steps, or with pins an odd number of inches apart, has no matching hole on a Manticore, Monster 2.0 or PR-5000.
- Side faces: Hydra’s taller uprights drop to 6″ side spacing through the middle. A side-mounted part that needs 2″ spacing only lines up near the top and bottom. Titan’s X-3 also uses 6″ side spacing.
Check how many pins an attachment uses and how far apart they are before you order it for a different brand. The rack attachment compatibility checklist covers pin spacing in more detail.
Bells of Steel attachments on other racks
Several Bells of Steel attachments are sold by tube and hole size rather than by rack name, which makes them the easiest to move across brands:
- Landmine Power Rack Attachment: one version for 5/8″ holes (Hydra and 2.3″ racks) and a Manticore version for 1″ holes that uses a mag pin.
- Rack-Attached Basketball Hoop: one model that “fits 3” x 3” (76.2 mm) tubing with ⅝” or 1” holes,” plus Bells of Steel’s original 2.3″ racks. It mounts with a bolted L-bracket.
- Utility Shackle: “Compatible with 3” x 3” racks with 5/8″ or 1″ holes,” and it bolts on.
The Smith Machine Rack Attachment is a different story. Bells of Steel lists it for Hydra and Manticore 4-post and 6-post racks at 47″ or 49″ wide, with upper brackets at the tops of the uprights and lower brackets on crossmembers or front foot stabilizers. It quotes 60 to 120 minutes to install, recommends two people, and rates it to 600 lb. Hydra flat-foot racks and squat stands mount it at a slight angle unless you add a long bolt kit and bushings. Anthony owned this attachment and described it in 10 Best Power Rack Attachments for Building Muscle at Home: it ran smoothly once installed, but installing it was a two-person job, lining up the bracket angles and hole spacing was frustrating, and it took up two full uprights. On another brand’s rack, expect that alignment work to be harder, not easier.
Third-party attachments on Hydra and Manticore
| Attachment | What the maker lists | On Hydra or Manticore |
|---|---|---|
| Exponent Edge Infinity Arm 2.0 (affiliate) | Names “Bells of Steel Hydra Series | 3″x3″”; separate 5/8″ and 1″ versions | Hydra is named. Manticore isn’t, though it matches the 3×3″, 1″ spec; ask Exponent |
| Bulletproof ISOLATOR 3×3 (affiliate) | 3×3, 2×3 and 2×2 uprights; choice of 1/2″, 5/8″, 3/4″ or 1″ pin | Bells of Steel isn’t named; pick 5/8″ for Hydra or 1″ for Manticore |
| Bridge BUILT Booster Hook | 3×3 racks with 5/8″, 3/4″ or 1″ holes; 400 lb | Spec match for both |
| Beyond Power Adaptive Rack Mount (VOLTRA I) (referral) | Uprights up to 4″ (102 mm); 5/8″ or 1″ holes | Size range, not a named rack list |
| Bulletproof VTS (affiliate) | “Works with” names Rogue, Titan and REP racks; “tested with 43″ max inside width” | Neither Hydra nor Manticore is named; ask Bulletproof first |
A spec match isn’t a promise. Check the exact pair in the Rack Attachment Fit Checker, and see the Beyond Power VOLTRA guide for VOLTRA mounting options.
The 2.3″ racks stay in their own lane
Bells of Steel’s Residential and Light Commercial racks use 2.3×2.3″ (60 mm) tube with 5/8″ holes, and Bells of Steel’s 2.3″ attachments are made for that tube. The FAQ also points out that 2.3″ tubing is uncommon, so owners will likely buy future attachments from Bells of Steel. The numbers explain why: a 2×2″ bracket (50.8 mm) is about 9 mm too narrow to slide on, and a 3×3″ bracket (76.2 mm) is about 16 mm too wide, which leaves a lot of slop even when the pin fits.
Two notes for 2.3″ owners. Bulletproof’s carriage shim kits (affiliate) page says the shims also work with “2.3 x 2.3 racks,” but the ISOLATOR’s own page lists 3×3, 2×3 and 2×2 uprights, so confirm with Bulletproof before ordering one for a 2.3″ rack. And if you own an older Bells of Steel rack that isn’t on the current site, measure it: Exponent Edge lists several older Bells of Steel racks (the Brute, Utility, Power Rack 4.1 and 5.1) as 2×3″, not 2.3″.
Cable attachments for Hydra and Manticore
- Kraken: a rack-mounted cable unit with a 210 lb stack. One cable runs 2:1, and both cables with the adapter run 1:1. Bells of Steel lists it for Hydra and Manticore 4-post and flat-foot racks at 24″, 30″ or 43″ deep, with separate 6-post versions, and says it fits “most 3” x 3” power racks.” The rack “must be bolted down or have Front Foot Stabilizers,” and the crossmembers have to be raised.
- Oblivyon 3×3 cable tower: a standalone tower with true 3×3″ (76.2 mm) 11-gauge uprights, “compatible with both the Hydra and Manticore rack and attachment lines,” running 2:1 or 1:1 with the included adapter.
- Functional Trainer Cable Tower: two 210 lb stacks at 2:1, with a cable adapter (sold separately) that combines both pulleys for 1:1. Its uprights take 2.3″ attachments, not Hydra or Manticore ones.
- Lat Pulldown Low Row: a 310 lb stack in 10 lb increments at a “True 1:1 ratio.”
At 2:1, you feel about half the selected weight and the handle travels twice as far as the stack. At 1:1, the pin number is roughly what you feel, plus friction. The cable pulley ratio calculator works it out for each of these settings.
Before you order
- Match the hole size. Hydra and 2.3″ racks take 5/8″. Manticore takes 1″ on the front and 5/8″ in the side keyholes.
- Count the pins. A second locking pin needs matching hole spacing on both racks.
- Check which face it mounts to. Hydra’s side holes are 6″ apart through the middle of tall uprights.
- Expect slack on 75 mm racks. Bells of Steel says its attachments fit them but not snugly.
- Keep 2.3″ racks on 2.3″ parts unless the maker names that tube size.
Compare full rack dimensions in the Power Rack Comparison Tool, and see Rogue Monster vs Monster Lite for how Rogue splits the same 5/8″ and 1″ standards.
The verdict
If you own a Hydra, single-hole 5/8″ attachments built for Rogue Monster Lite or REP PR-4000 are your best cross-brand bet. If you own a Manticore, look at 1″ attachments for Rogue Monster 2.0 or REP PR-5000, and remember your side keyholes take 5/8″ Hydra parts too. Two-pin attachments, side-mounted parts and anything sleeve-shaped need a closer check. If you own a 2.3″ Bells of Steel rack, stick with Bells of Steel’s 2.3″ attachments.
Specifications checked against manufacturer pages on October 17, 2026. Manufacturers change specs; confirm on the product page before ordering.