An attachment fits when two numbers match your rack: the tubing size (how wide the upright is) and the hole size. Every B.o.S. rack uses square tubing in either 2.3" x 2.3" (60 x 60 mm) or 3" x 3" (76.2 x 76.2 mm), with holes that are either 5/8" or 1". A 3" attachment can technically go on a 2.3" rack, but it wobbles and may not pin down properly, so skip it. Thanks to keyhole holes, 5/8" Hydra attachments fit Manticore racks, which makes upgrading painless.
Want the TL;DR? Press play and let B.o.S. Coach Mo and Coach Aleesha walk through attachment fitment in under 4 minutes. Then read on for more of the nitty gritty: charts, mix-and-match rules, and cross-brand fitment.
Here's the question that shows up more than any other when someone shops for rack attachments: "Will it fit?" Fair question. Nobody wants a shiny new dip station that hangs off the upright like a loose tooth.
This guide settles the 2x2 vs 3x3 power rack question with the two specs that decide fitment, a chart for every B.o.S. rack line, and what happens when you mix and match sizes, or even brands.
What two numbers decide if an attachment fits?
Forget the marketing photos. Fitment comes down to two measurements, and both have to match the attachment you're buying.
1. Tubing size
This is the width of the upright, the vertical post the attachment slides onto. B.o.S. racks are square, so both sides measure the same.
2. Hole size
This is the diameter of the holes running up the upright, where the pins go to lock an attachment in place.
Not sure what you've got? Grab a tape measure. Measuring the width of an upright takes about as long as reading this sentence, and it beats guessing every time. Metric tape? No problem, the tubing sizes in millimetres are right there in the chart below.
Which tubing and hole sizes do B.o.S. racks use?
Shop around and you'll see racks sold as 2x2, 2x3, or 3x3. B.o.S. keeps it simple: every rack is square, in one of two tubing sizes, 2.3" x 2.3" or 3" x 3". Holes come in two sizes too: 5/8" and 1".
That gives you three rack families, each with its own combo. Here's the fitment chart.
| Rack line | Tubing size | Hole size | Look for attachments labelled |
|---|---|---|---|
| Residential and Light Commercial racks | 2.3" x 2.3" 60 x 60 mm |
5/8" | 2.3" x 2.3", 5/8" holes |
| Hydra racks | 3" x 3" 76.2 x 76.2 mm |
5/8" | Hydra, or 3" x 3" with 5/8" holes |
| Manticore racks | 3" x 3" 76.2 x 76.2 mm |
1" plus keyhole holes on the side that combine 1" and 5/8" |
Manticore, or 3" x 3" with 1" holes. 5/8" Hydra attachments also fit, thanks to the keyholes. |
Bottom line: Hydra and Manticore share the same 3" x 3" tubing. The difference is the hole size, 5/8" on Hydra and 1" on Manticore.
A rack by any other name
Fitment doesn't care about the logo on the upright, or whether the listing calls it a 2x2 or a 3x3. What matters is the steel: if a rack from another brand truly measures the same as a B.o.S. rack, 2.3" x 2.3" or 3" x 3" tubing with matching 5/8" or 1" holes, the attachment should slot right on.
So measure the tubing, measure the holes, and match both numbers. If they line up, you're good to go, no matter whose name is on the rack. Not sure? The B.o.S. support team is happy to double-check your measurements.
What makes the Manticore system different?
Manticore racks have the bigger 1" holes, but there's a twist. The sides of the uprights have keyhole-shaped holes that combine a 1" opening with a 5/8" opening.
Translation: attachments built for either hole size have a place to pin in. It's the rack equivalent of a universal remote, minus the hunt for batteries.
Can you use a 3x3 attachment on a 2.3" x 2.3" B.o.S. rack?
Technically, yes. Should you? Not really, and B.o.S. doesn't recommend it. Two problems show up the second the attachment goes on.
1. It wobbles
A 3" sleeve on a 2.3" upright leaves a gap all the way around. That extra space lets the attachment shift and rattle, which is not the vibe you want under a loaded barbell.
2. The pin holes may not line up
The safety pin hole on the attachment might not match up with the holes on the rack. If the pin can't go through cleanly, the attachment can't be properly secured.
Wobbly and hard to lock down is a hard pass. Match the attachment to your rack's tubing and save yourself the stress.
Do Hydra attachments fit a Manticore rack?
Yes, and this is great news for anyone planning to upgrade. Both systems use 3" x 3" tubing, and the keyhole holes on Manticore uprights include a 5/8" opening, so 5/8" Hydra attachments have a spot to pin in.
Put a Hydra dip attachment next to a Manticore one on a Manticore rack and both do the job. The Hydra version can lift slightly when pushed upward, but that doesn't affect training: your force goes down into the attachment, so it stays seated. The Manticore version sits nice and stable with no play at all.
So if you start on Hydra and move up to Manticore later, every Hydra attachment you own comes with you. No lock-in, no starting from scratch, no awkward garage sale.
Fitment at a glance: what works on what?
| Attachment | Rack | Does it fit? |
|---|---|---|
| 2.3" x 2.3", 5/8" holes | Residential or Light Commercial (2.3" x 2.3", 5/8") | Yes, matched fit |
| 3" x 3" (any) | Residential or Light Commercial (2.3" x 2.3", 5/8") | Technically mounts, but not recommended: it wobbles and the pin hole may not line up |
| Hydra (3" x 3", 5/8") | Hydra (3" x 3", 5/8") | Yes, matched fit |
| Hydra (3" x 3", 5/8") | Manticore (3" x 3", 1" plus keyholes) | Yes, the keyholes take 5/8" pins. It may lift slightly upward, but it stays in place under load |
| Manticore (3" x 3", 1") | Manticore (3" x 3", 1") | Yes, matched fit and the most stable |
| Any brand, same tubing and hole size | Any brand, same tubing and hole size | Should be good to go. Match both numbers first |
Bottom line: match the tubing first, then the holes. Combo not on this chart? Check with the B.o.S. support team before ordering.
Which pins come with each attachment?
Pins are the unsung heroes of fitment. Attachments built for 5/8" holes come with standard safety pins by default. Manticore attachments come with magnetic pins out of the box, which are nicer and easier to use.
Want that upgrade on your 5/8" attachments? Magnetic Rack Attachment Pins are sold separately.
Sizing up the room instead of the rack? See the best racks for small garages and low ceilings for ceiling height, footprint, and folding options.
Still deciding on the rack itself? The power rack vs squat rack guide covers the differences in safety and versatility.
Residential Power Rack
The 2.3" x 2.3" (60 mm) option with 5/8" holes. Pair it with attachments made for the same size for a snug, secure fit.
Shop Residential Rack
Hydra Four Post Power Rack
3" x 3" (76.2 mm) tubing with 5/8" holes. Every Hydra attachment you add also fits a Manticore rack if you upgrade later.
Build Your Hydra
Manticore Four Post Power Rack
3" x 3" (76.2 mm) tubing with 1" holes and keyholes on the side. Takes Manticore and 5/8" Hydra attachments.
Shop Manticore RackRack attachment fitment FAQ
How do you know which size rack you have?
Measure the width of an upright for the tubing size, and check the diameter of the holes. Both numbers need to match the attachment.
What is the difference between a 2x2 and a 3x3 power rack?
The width of the uprights. B.o.S. racks come in 2.3" x 2.3" (60 mm, Residential and Light Commercial) or 3" x 3" (76.2 mm, Hydra and Manticore). Attachments are built for one tubing size, so they need to match.
Can you put 3x3 rack attachments on a 2.3" x 2.3" rack?
It can technically go on, but it isn't recommended. The gap makes the attachment wobble, and the pin hole may not line up well enough to secure it.
What hole size do B.o.S. racks have?
Residential, Light Commercial, and Hydra racks have 5/8" holes. Manticore racks have 1" holes, plus keyhole holes on the side that combine 1" and 5/8".
Will Hydra attachments work after upgrading to Manticore?
Yes. The keyhole holes on Manticore uprights take 5/8" pins, so Hydra attachments fit. They can lift slightly when pushed upward, but they stay in place during training because your force goes down.
Do B.o.S. attachments fit racks from other brands?
If the other rack has the same tubing size and hole size, they should. Measure both and match them. The same logic works in reverse for attachments from other brands.
Do attachments come with magnetic pins?
Manticore attachments come with magnetic pins by default. Attachments for 5/8" holes come with standard safety pins, and magnetic pins can be purchased separately.
Still not sure an attachment will fit? Send your rack details to the B.o.S. support team and they'll point you to the right match. Shopping for the rack itself? Browse the full lineup of power racks.
